Add initial checker framework configuration

build.gradle

@@ -24,6 +24,9 @@ plugins {
 
  id 'checkstyle'
 
+ // Homepage: https://github.com/kelloggm/checkerframework-gradle-plugin
+ id 'org.checkerframework' version '0.6.40'
+
  id 'project-report'
 
  id 'idea'
@@ -38,6 +41,8 @@ apply plugin: XjcPlugin
 
 apply from: 'eclipse.gradle'
 
+apply plugin: 'org.checkerframework'
+
 group = "org.jabref"
 version = project.findProperty('projVersion') ?: '100.0.0'
 
@@ -322,6 +327,11 @@ dependencies {
  rewrite("org.openrewrite.recipe:rewrite-testing-frameworks")
  rewrite("org.openrewrite.recipe:rewrite-migrate-java")
 
+ // checker framework
+ compileOnly 'org.checkerframework:checker-qual:3.44.0'
+ testCompileOnly 'org.checkerframework:checker-qual:3.44.0'
+ checkerFramework 'org.checkerframework:checker:3.44.0'
+
  configurations.checkstyle {
  resolutionStrategy.capabilitiesResolution.withCapability("com.google.collections:google-collections") {
  select("com.google.guava:guava:0")
@@ -614,6 +624,13 @@ checkstyle {
  sourceSets = []
 }
 
+checkerFramework {
+ checkers = [
+ 'org.checkerframework.checker.nullness.NullnessChecker'
+ ]
+ excludeTests = true
+}
+
 rewrite {
  activeRecipe(
  'org.jabref.config.rewrite.cleanup'

src/main/java/module-info.java

@@ -143,6 +143,7 @@
  uses org.eclipse.jgit.lib.GpgSigner;
 
  requires transitive org.jspecify;
+ requires org.checkerframework.checker.qual;
 
  // other libraries
  requires org.antlr.antlr4.runtime;

src/main/java/org/jabref/logic/pdf/search/PdfIndexer.java

@@ -55,8 +55,7 @@ public class PdfIndexer {
 
  private final FilePreferences filePreferences;
 
- @Nullable
- private final Directory indexDirectory;
+ private final @Nullable Directory indexDirectory;
 
  private IndexReader reader;