diff --git a/packages/js/core/src/interfaces/uri-resolver.ts b/packages/js/core/src/interfaces/uri-resolver.ts
index 2be4064cbf..9690c02299 100644
--- a/packages/js/core/src/interfaces/uri-resolver.ts
+++ b/packages/js/core/src/interfaces/uri-resolver.ts
@@ -4,8 +4,8 @@ import { Tracer } from "@polywrap/tracing-js";
 import { Result } from "@polywrap/result";
 
 export interface MaybeUriOrManifest {
-  uri?: string;
-  manifest?: Uint8Array;
+  uri?: string | null;
+  manifest?: Uint8Array | null;
 }
 
 export const module = {
@@ -32,8 +32,8 @@ export const module = {
       invoker: Invoker,
       wrapper: Uri,
       path: string
-    ): Promise<Result<Uint8Array | undefined, WrapError>> => {
-      return invoker.invoke<Uint8Array | undefined>({
+    ): Promise<Result<Uint8Array | null, WrapError>> => {
+      return invoker.invoke<Uint8Array | null>({
         uri: wrapper.uri,
         method: "getFile",
         args: {
diff --git a/packages/js/uri-resolver-extensions/src/UriResolverExtensionFileReader.ts b/packages/js/uri-resolver-extensions/src/UriResolverExtensionFileReader.ts
index b367d8df4d..67145192fe 100644
--- a/packages/js/uri-resolver-extensions/src/UriResolverExtensionFileReader.ts
+++ b/packages/js/uri-resolver-extensions/src/UriResolverExtensionFileReader.ts
@@ -34,7 +34,7 @@ export class UriResolverExtensionFileReader implements IFileReader {
       path
     );
     if (!result.ok) return result;
-    if (result.value === undefined) {
+    if (!result.value) {
       return ResultErr(new Error(`File not found at ${path}`));
     }
     return {