diff --git a/lib/adapters/apply-edit-adapter.ts b/lib/adapters/apply-edit-adapter.ts
index 6d89ceb..695e938 100644
--- a/lib/adapters/apply-edit-adapter.ts
+++ b/lib/adapters/apply-edit-adapter.ts
@@ -40,7 +40,7 @@ export default class ApplyEditAdapter {
       }),
     );
 
-    const checkpoints = [];
+    const checkpoints: Array<{ buffer: TextBuffer, checkpoint: number}> = [];
     try {
       for (let i = 0; i < editors.length; i++) {
         const editor = editors[i] as TextEditor;
@@ -52,7 +52,7 @@ export default class ApplyEditAdapter {
         const buffer = editor.getBuffer();
         const checkpoint = buffer.createCheckpoint();
         checkpoints.push({buffer, checkpoint});
-        let prevEdit = null;
+        let prevEdit: atomIde.TextEdit | null = null;
         for (const edit of edits) {
           ApplyEditAdapter.validateEdit(buffer, edit, prevEdit);
           buffer.setTextInRange(edit.oldRange, edit.newText);
@@ -74,9 +74,13 @@ export default class ApplyEditAdapter {
   }
 
   // Private: Do some basic sanity checking on the edit ranges.
-  private static validateEdit(buffer: TextBuffer, edit: atomIde.TextEdit, prevEdit: atomIde.TextEdit | null): void {
+  private static validateEdit(
+    buffer: TextBuffer,
+    edit: atomIde.TextEdit,
+    prevEdit: atomIde.TextEdit | null,
+  ): void {
     const path = buffer.getPath() || '';
-    if (prevEdit != null && edit.oldRange.end.compare(prevEdit.oldRange.start) > 0) {
+    if (prevEdit && edit.oldRange.end.compare(prevEdit.oldRange.start) > 0) {
       throw Error(`Found overlapping edit ranges in ${path}`);
     }
     const startRow = edit.oldRange.start.row;
diff --git a/lib/adapters/autocomplete-adapter.ts b/lib/adapters/autocomplete-adapter.ts
index e68a782..f823ba0 100644
--- a/lib/adapters/autocomplete-adapter.ts
+++ b/lib/adapters/autocomplete-adapter.ts
@@ -267,11 +267,11 @@ export default class AutocompleteAdapter {
   // * `editor` An Atom {TextEditor} used to obtain the necessary text replacement.
   // * `suggestion` An {atom$AutocompleteSuggestion} to set the replacementPrefix and text properties of.
   public static applyTextEditToSuggestion(
-    textEdit: TextEdit | null,
+    textEdit: TextEdit | undefined,
     editor: TextEditor,
     suggestion: AutocompleteSuggestion,
   ): void {
-    if (textEdit != null) {
+    if (textEdit) {
       suggestion.replacementPrefix = editor.getTextInBufferRange(Convert.lsRangeToAtomRange(textEdit.range));
       suggestion.text = textEdit.newText;
     }
@@ -296,7 +296,7 @@ export default class AutocompleteAdapter {
   //
   // Returns a {String} containing the AutoComplete+ suggestion type equivalent
   // to the given completion kind.
-  public static completionKindToSuggestionType(kind: number | null): string {
+  public static completionKindToSuggestionType(kind: number | undefined): string {
     switch (kind) {
       case CompletionItemKind.Constant:
         return 'constant';
diff --git a/lib/adapters/code-action-adapter.ts b/lib/adapters/code-action-adapter.ts
index 330491d..43a5ec4 100644
--- a/lib/adapters/code-action-adapter.ts
+++ b/lib/adapters/code-action-adapter.ts
@@ -27,7 +27,7 @@ export default class CodeActionAdapter {
   public static async getCodeActions(
     connection: LanguageClientConnection,
     serverCapabilities: ServerCapabilities,
-    linterAdapter: LinterPushV2Adapter | null,
+    linterAdapter: LinterPushV2Adapter | undefined ,
     editor: TextEditor,
     range: Range,
     diagnostics: atomIde.Diagnostic[],
diff --git a/lib/adapters/datatip-adapter.ts b/lib/adapters/datatip-adapter.ts
index 7ef8bd8..d6d1c26 100644
--- a/lib/adapters/datatip-adapter.ts
+++ b/lib/adapters/datatip-adapter.ts
@@ -88,5 +88,8 @@ export default class DatatipAdapter {
         value: markedString.value,
       };
     }
+
+    // Catch-all case
+    return { type: 'markdown', value: markedString.toString() };
   }
 }
diff --git a/lib/adapters/document-sync-adapter.ts b/lib/adapters/document-sync-adapter.ts
index 05f066b..7208a68 100644
--- a/lib/adapters/document-sync-adapter.ts
+++ b/lib/adapters/document-sync-adapter.ts
@@ -64,7 +64,7 @@ export default class DocumentSyncAdapter {
   //                    indicating whether this adapter should care about the contents of the editor.
   constructor(
     connection: LanguageClientConnection,
-    documentSyncKind: TextDocumentSyncOptions | number | null,
+    documentSyncKind: TextDocumentSyncOptions | number | undefined,
     editorSelector: (editor: TextEditor) => boolean,
   ) {
     this._connection = connection;
@@ -129,7 +129,7 @@ export default class DocumentSyncAdapter {
     );
   }
 
-  public getEditorSyncAdapter(editor: TextEditor): TextEditorSyncAdapter | null {
+  public getEditorSyncAdapter(editor: TextEditor): TextEditorSyncAdapter | undefined {
     return this._editors.get(editor);
   }
 }
diff --git a/lib/adapters/linter-push-v2-adapter.ts b/lib/adapters/linter-push-v2-adapter.ts
index 1bfdeef..ab08724 100644
--- a/lib/adapters/linter-push-v2-adapter.ts
+++ b/lib/adapters/linter-push-v2-adapter.ts
@@ -113,7 +113,7 @@ export default class LinterPushV2Adapter {
     if (path != null) {
       const diagnosticCodes = this._diagnosticCodes.get(path);
       if (diagnosticCodes != null) {
-        return diagnosticCodes.get(getCodeKey(range, text));
+        return diagnosticCodes.get(getCodeKey(range, text)) || null;
       }
     }
     return null;
@@ -121,5 +121,5 @@ export default class LinterPushV2Adapter {
 }
 
 function getCodeKey(range: atom.Range, text: string): string {
-  return [].concat(...range.serialize(), text).join(',');
+  return ([] as any[]).concat(...range.serialize(), text).join(',');
 }
diff --git a/lib/adapters/outline-view-adapter.ts b/lib/adapters/outline-view-adapter.ts
index 3bffeb0..3f7bcc4 100644
--- a/lib/adapters/outline-view-adapter.ts
+++ b/lib/adapters/outline-view-adapter.ts
@@ -115,24 +115,27 @@ export default class OutlineViewAdapter {
       return null;
     }
 
-    let parent = null;
+    let parent: atomIde.OutlineTree | undefined;
     for (const candidate of candidates) {
       if (
         candidate !== child &&
         candidate.startPosition.isLessThanOrEqual(child.startPosition) &&
-        (candidate.endPosition == null || candidate.endPosition.isGreaterThanOrEqual(child.endPosition))
+        (candidate.endPosition === undefined ||
+          (child.endPosition && candidate.endPosition.isGreaterThanOrEqual(child.endPosition)))
       ) {
         if (
-          parent == null ||
+          parent === undefined ||
           (parent.startPosition.isLessThanOrEqual(candidate.startPosition) ||
-            (parent.endPosition != null && parent.endPosition.isGreaterThanOrEqual(candidate.endPosition)))
+            (parent.endPosition != null &&
+              candidate.endPosition &&
+              parent.endPosition.isGreaterThanOrEqual(candidate.endPosition)))
         ) {
           parent = candidate;
         }
       }
     }
 
-    return parent;
+    return parent || null;
   }
 
   // Public: Convert an individual {SymbolInformation} from the language server
diff --git a/lib/adapters/signature-help-adapter.ts b/lib/adapters/signature-help-adapter.ts
index 95003a1..dfe9b67 100644
--- a/lib/adapters/signature-help-adapter.ts
+++ b/lib/adapters/signature-help-adapter.ts
@@ -31,8 +31,8 @@ export default class SignatureHelpAdapter {
     const {signatureHelpProvider} = this._capabilities;
     assert(signatureHelpProvider != null);
 
-    let triggerCharacters = null;
-    if (Array.isArray(signatureHelpProvider.triggerCharacters)) {
+    let triggerCharacters: Set<string> | undefined;
+    if (signatureHelpProvider && Array.isArray(signatureHelpProvider.triggerCharacters)) {
       triggerCharacters = new Set(signatureHelpProvider.triggerCharacters);
     }
 
diff --git a/lib/auto-languageclient.ts b/lib/auto-languageclient.ts
index 27d8aea..b4299cb 100644
--- a/lib/auto-languageclient.ts
+++ b/lib/auto-languageclient.ts
@@ -4,13 +4,13 @@ import * as rpc from 'vscode-jsonrpc';
 import * as path from 'path';
 import * as atomIde from 'atom-ide';
 import * as linter from 'atom-linter';
-import * as stream from 'stream';
 import { Socket } from 'net';
-import { EventEmitter } from 'events';
 import { ConsoleLogger, NullLogger, Logger } from './logger';
-import { ServerManager, ActiveServer } from './server-manager.js';
+import { LanguageServerProcess, ServerManager, ActiveServer } from './server-manager.js';
 import Convert from './convert.js';
 
+export { LanguageServerProcess };
+
 import {
   AutocompleteDidInsert,
   AutocompleteProvider,
@@ -39,21 +39,6 @@ import SignatureHelpAdapter from './adapters/signature-help-adapter';
 
 export type ConnectionType = 'stdio' | 'socket' | 'ipc';
 
-// Public: Defines the minimum surface area for an object that resembles a
-// ChildProcess.  This is used so that language packages with alternative
-// language server process hosting strategies can return something compatible
-// with AutoLanguageClient.startServerProcess.
-export interface LanguageServerProcess extends EventEmitter {
-  stdin: stream.Writable;
-  stdout: stream.Readable;
-  stderr: stream.Readable;
-  pid: number;
-
-  kill(signal?: string): void;
-  on(event: 'error', listener: (err: Error) => void): this;
-  on(event: 'exit', listener: (code: number, signal: string) => void): this;
-}
-
 // Public: AutoLanguageClient provides a simple way to have all the supported
 // Atom-IDE services wired up entirely for you by just subclassing it and
 // implementing startServerProcess/getGrammarScopes/getLanguageName and
@@ -62,7 +47,7 @@ export default class AutoLanguageClient {
   private _disposable = new CompositeDisposable();
   private _serverManager: ServerManager;
   private _linterDelegate: linter.V2IndieDelegate;
-  private _signatureHelpRegistry: atomIde.SignatureHelpRegistry;
+  private _signatureHelpRegistry: atomIde.SignatureHelpRegistry | null;
   private _lastAutocompleteRequest: AutocompleteRequest;
   private _isDeactivating: boolean;
 
diff --git a/lib/convert.ts b/lib/convert.ts
index f9808d7..38744d6 100644
--- a/lib/convert.ts
+++ b/lib/convert.ts
@@ -159,7 +159,7 @@ export default class Convert {
       case 'deleted':
         return [{uri: Convert.pathToUri(fileEvent.path), type: ls.FileChangeType.Deleted}];
       case 'renamed': {
-        const results = [];
+        const results: Array<{ uri: string, type: ls.FileChangeType }> = [];
         if (fileEvent.oldPath) {
           results.push({uri: Convert.pathToUri(fileEvent.oldPath || ''), type: ls.FileChangeType.Deleted});
         }
diff --git a/lib/download-file.ts b/lib/download-file.ts
index a367249..e9f3950 100644
--- a/lib/download-file.ts
+++ b/lib/download-file.ts
@@ -31,7 +31,7 @@ export default (async function downloadFile(
     throw Error('No response body');
   }
 
-  const finalLength = length || parseInt(response.headers.get('Content-Length' || '0'), 10);
+  const finalLength = length || parseInt(response.headers.get('Content-Length') || '0', 10);
   const reader = body.getReader();
   const writer = fs.createWriteStream(targetFile);
 
@@ -72,7 +72,7 @@ async function streamWithProgress(
       writer.write(Buffer.from(chunk));
       if (progressCallback != null) {
         bytesDone += chunk.byteLength;
-        const percent: number = length === 0 ? null : Math.floor(bytesDone / length * 100);
+        const percent: number | undefined = length === 0 ? undefined : Math.floor(bytesDone / length * 100);
         progressCallback(bytesDone, percent);
       }
     }
diff --git a/lib/server-manager.ts b/lib/server-manager.ts
index 3fee2a6..a6ad187 100644
--- a/lib/server-manager.ts
+++ b/lib/server-manager.ts
@@ -1,20 +1,37 @@
 import { Logger } from './logger';
+import { EventEmitter } from 'events';
 import LinterPushV2Adapter from './adapters/linter-push-v2-adapter';
 import DocumentSyncAdapter from './adapters/document-sync-adapter';
 import SignatureHelpAdapter from './adapters/signature-help-adapter';
 
 import * as path from 'path';
+import * as stream from 'stream';
 import * as cp from 'child_process';
 import * as ls from './languageclient';
 import * as atomIde from 'atom-ide';
 import Convert from './convert';
 import { CompositeDisposable, ProjectFileEvent, TextEditor } from 'atom';
 
+// Public: Defines the minimum surface area for an object that resembles a
+// ChildProcess.  This is used so that language packages with alternative
+// language server process hosting strategies can return something compatible
+// with AutoLanguageClient.startServerProcess.
+export interface LanguageServerProcess extends EventEmitter {
+  stdin: stream.Writable;
+  stdout: stream.Readable;
+  stderr: stream.Readable;
+  pid: number;
+
+  kill(signal?: string): void;
+  on(event: 'error', listener: (err: Error) => void): this;
+  on(event: 'exit', listener: (code: number, signal: string) => void): this;
+}
+
 // The necessary elements for a server that has started or is starting.
 export interface ActiveServer {
   disposable: CompositeDisposable;
   projectPath: string;
-  process: cp.ChildProcess;
+  process: LanguageServerProcess;
   connection: ls.LanguageClientConnection;
   capabilities: ls.ServerCapabilities;
   linterPushV2?: LinterPushV2Adapter;
@@ -269,7 +286,7 @@ export class ServerManager {
     if (filePath == null) {
       return null;
     }
-    return this._normalizedProjectPaths.find((d) => filePath.startsWith(d));
+    return this._normalizedProjectPaths.find((d) => filePath.startsWith(d)) || null;
   }
 
   public updateNormalizedProjectPaths(): void {
@@ -293,7 +310,7 @@ export class ServerManager {
     }
 
     for (const activeServer of this._activeServers) {
-      const changes = [];
+      const changes: ls.FileEvent[] = [];
       for (const fileEvent of fileEvents) {
         if (fileEvent.path.startsWith(activeServer.projectPath) && this._changeWatchedFileFilter(fileEvent.path)) {
           changes.push(Convert.atomFileEventToLSFileEvents(fileEvent)[0]);
diff --git a/test/adapters/autocomplete-adapter.test.ts b/test/adapters/autocomplete-adapter.test.ts
index ad27356..df6d61f 100644
--- a/test/adapters/autocomplete-adapter.test.ts
+++ b/test/adapters/autocomplete-adapter.test.ts
@@ -20,7 +20,7 @@ describe('AutoCompleteAdapter', () => {
       capabilities: {completionProvider: { }},
       connection: new ls.LanguageClientConnection(createSpyConnection()),
       disposable: new CompositeDisposable(),
-      process: undefined,
+      process: undefined as any,
       projectPath: '/',
     };
   }
@@ -279,7 +279,7 @@ describe('AutoCompleteAdapter', () => {
 
     it('does not do anything if there is no textEdit', () => {
       const completionItem: AutocompleteSuggestion = {};
-      AutoCompleteAdapter.applyTextEditToSuggestion(null, new TextEditor(), completionItem);
+      AutoCompleteAdapter.applyTextEditToSuggestion(undefined, new TextEditor(), completionItem);
       expect(completionItem).deep.equals({});
     });
 
@@ -315,7 +315,7 @@ describe('AutoCompleteAdapter', () => {
     });
 
     it('defaults to "value"', () => {
-      const result = AutoCompleteAdapter.completionKindToSuggestionType(null);
+      const result = AutoCompleteAdapter.completionKindToSuggestionType(undefined);
       expect(result).equals('value');
     });
   });
diff --git a/test/adapters/code-highlight-adapter.test.ts b/test/adapters/code-highlight-adapter.test.ts
index 09f47d1..154776e 100644
--- a/test/adapters/code-highlight-adapter.test.ts
+++ b/test/adapters/code-highlight-adapter.test.ts
@@ -50,8 +50,10 @@ describe('CodeHighlightAdapter', () => {
       expect(highlightStub.called).to.be.true;
 
       invariant(result != null);
-      expect(result.length).to.equal(1);
-      expect(result[0].isEqual(new Range([0, 1], [0, 2]))).to.be.true;
+      if (result) {
+        expect(result.length).to.equal(1);
+        expect(result[0].isEqual(new Range([0, 1], [0, 2]))).to.be.true;
+      }
     });
 
     it('throws if document highlights are not supported', async () => {
diff --git a/test/adapters/datatip-adapter.test.ts b/test/adapters/datatip-adapter.test.ts
index 89eebc0..54e5b62 100644
--- a/test/adapters/datatip-adapter.test.ts
+++ b/test/adapters/datatip-adapter.test.ts
@@ -48,21 +48,23 @@ describe('DatatipAdapter', () => {
       expect(datatip).to.be.ok;
       invariant(datatip != null);
 
-      expect(datatip.range.start.row).equal(0);
-      expect(datatip.range.start.column).equal(1);
-      expect(datatip.range.end.row).equal(0);
-      expect(datatip.range.end.column).equal(2);
+      if (datatip) {
+        expect(datatip.range.start.row).equal(0);
+        expect(datatip.range.start.column).equal(1);
+        expect(datatip.range.end.row).equal(0);
+        expect(datatip.range.end.column).equal(2);
 
-      expect(datatip.markedStrings).to.have.lengthOf(2);
-      expect(datatip.markedStrings[0]).eql({type: 'markdown', value: 'test'});
+        expect(datatip.markedStrings).to.have.lengthOf(2);
+        expect(datatip.markedStrings[0]).eql({type: 'markdown', value: 'test'});
 
-      const snippet = datatip.markedStrings[1];
-      expect(snippet.type).equal('snippet');
-      invariant(snippet.type === 'snippet');
-      expect((snippet as any).grammar.scopeName).equal('text.plain.null-grammar');
-      expect(snippet.value).equal('test snippet');
+        const snippet = datatip.markedStrings[1];
+        expect(snippet.type).equal('snippet');
+        invariant(snippet.type === 'snippet');
+        expect((snippet as any).grammar.scopeName).equal('text.plain.null-grammar');
+        expect(snippet.value).equal('test snippet');
 
-      expect(grammarSpy.calledWith('source.testlang')).to.be.true;
+        expect(grammarSpy.calledWith('source.testlang')).to.be.true;
+      }
     });
   });
 });
diff --git a/test/adapters/document-sync-adapter.test.ts b/test/adapters/document-sync-adapter.test.ts
index b57aca9..916dbbb 100644
--- a/test/adapters/document-sync-adapter.test.ts
+++ b/test/adapters/document-sync-adapter.test.ts
@@ -49,7 +49,7 @@ describe('DocumentSyncAdapter', () => {
 
   describe('constructor', () => {
     function create(textDocumentSync) {
-      return new DocumentSyncAdapter(null, textDocumentSync, () => false);
+      return new DocumentSyncAdapter(null as any, textDocumentSync, () => false);
     }
 
     it('sets _documentSyncKind correctly Incremental for v2 capabilities', () => {
diff --git a/test/adapters/outline-view-adapter.test.ts b/test/adapters/outline-view-adapter.test.ts
index 8212eb8..b568560 100644
--- a/test/adapters/outline-view-adapter.test.ts
+++ b/test/adapters/outline-view-adapter.test.ts
@@ -121,11 +121,22 @@ describe('OutlineViewAdapter', () => {
           containerName: 'duplicate',
         },
       ];
+
       const result = OutlineViewAdapter.createOutlineTrees(sourceItems);
       expect(result.length).to.equal(1);
-      expect(result[0].endPosition.row).to.equal(10);
-      expect(result[0].children.length).to.equal(1);
-      expect(result[0].children[0].endPosition.row).to.equal(7);
+
+      const outline = result[0];
+      expect(outline.endPosition).to.not.be.undefined;
+      if (outline.endPosition) {
+        expect(outline.endPosition.row).to.equal(10);
+        expect(outline.children.length).to.equal(1);
+
+        const outlineChild = outline.children[0];
+        expect(outlineChild.endPosition).to.not.be.undefined;
+        if (outlineChild.endPosition) {
+          expect(outlineChild.endPosition.row).to.equal(7);
+        }
+      }
     });
 
     it('parents to the innnermost named container', () => {
@@ -141,11 +152,29 @@ describe('OutlineViewAdapter', () => {
       ];
       const result = OutlineViewAdapter.createOutlineTrees(sourceItems);
       expect(result.length).to.equal(1);
-      expect(result[0].endPosition.row).to.equal(10);
-      expect(result[0].children.length).to.equal(1);
-      expect(result[0].children[0].endPosition.row).to.equal(8);
-      expect(result[0].children[0].children.length).to.equal(1);
-      expect(result[0].children[0].children[0].endPosition.row).to.equal(5);
+
+      const outline = result[0];
+      expect(outline).to.not.be.undefined;
+      if (outline) {
+        expect(outline.endPosition).to.not.be.undefined;
+        if (outline.endPosition) {
+          expect(outline.endPosition.row).to.equal(10);
+          expect(outline.children.length).to.equal(1);
+
+          const outlineChild = outline.children[0];
+          expect(outlineChild.endPosition).to.not.be.undefined;
+          if (outlineChild.endPosition) {
+            expect(outlineChild.endPosition.row).to.equal(8);
+            expect(outlineChild.children.length).to.equal(1);
+
+            const outlineGrandChild = outlineChild.children[0];
+            expect(outlineGrandChild.endPosition).to.not.be.undefined;
+            if (outlineGrandChild.endPosition) {
+              expect(outlineGrandChild.endPosition.row).to.equal(5);
+            }
+          }
+        }
+      }
     });
   });
 
@@ -156,12 +185,19 @@ describe('OutlineViewAdapter', () => {
       expect(result.icon).to.equal('type-class');
       expect(result.representativeName).to.equal('Program');
       expect(result.children).to.deep.equal([]);
-      expect(result.tokenizedText[0].kind).to.equal('type');
-      expect(result.tokenizedText[0].value).to.equal('Program');
-      expect(result.startPosition.row).to.equal(1);
-      expect(result.startPosition.column).to.equal(2);
-      expect(result.endPosition.row).to.equal(3);
-      expect(result.endPosition.column).to.equal(4);
+      expect(result.tokenizedText).to.not.be.undefined;
+      if (result.tokenizedText) {
+        const resultTokenixedText = result.tokenizedText[0];
+        expect(result.tokenizedText[0].kind).to.equal('type');
+        expect(result.tokenizedText[0].value).to.equal('Program');
+        expect(result.startPosition.row).to.equal(1);
+        expect(result.startPosition.column).to.equal(2);
+        expect(result.endPosition).to.not.be.undefined;
+        if (result.endPosition) {
+          expect(result.endPosition.row).to.equal(3);
+          expect(result.endPosition.column).to.equal(4);
+        }
+      }
     });
   });
 });
diff --git a/tsconfig.json b/tsconfig.json
index 95fc7ac..aca5daa 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -7,6 +7,7 @@
         "declaration": true,
         "inlineSources": true,
         "inlineSourceMap": true,
+        "strictNullChecks": true,
         "baseUrl": "./",
         "paths": {
             "atom-ide": [
diff --git a/typings/atom-ide/index.d.ts b/typings/atom-ide/index.d.ts
index d033c3c..07aefae 100644
--- a/typings/atom-ide/index.d.ts
+++ b/typings/atom-ide/index.d.ts
@@ -178,7 +178,7 @@ export interface CodeActionProvider {
     editor: TextEditor,
     range: Range,
     diagnostics: Diagnostic[],
-  ): Promise<CodeAction[]>;
+  ): Promise<CodeAction[] | null>;
 }
 
 export interface BusySignalOptions {