diff --git a/.github/workflows/code_quality.yml b/.github/workflows/code_quality.yml
index a3bd4d9a1b2..c3aecbc0256 100644
--- a/.github/workflows/code_quality.yml
+++ b/.github/workflows/code_quality.yml
@@ -9,6 +9,22 @@ on:
       - 'KeY-*'
 
 jobs:
+  checkerFramework:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up JDK 21
+        uses: actions/setup-java@v3
+        with:
+          java-version: 21
+          distribution: 'corretto'
+          cache: 'gradle'
+      - name: Build with Gradle
+        uses: gradle/gradle-build-action@v2.4.2
+        with:
+          arguments: -DENABLE_NULLNESS=true compileTest
+
+
   qodana:
     runs-on: ubuntu-latest
     steps:
diff --git a/build.gradle b/build.gradle
index 7858cbf268d..f29672c05f7 100644
--- a/build.gradle
+++ b/build.gradle
@@ -83,8 +83,8 @@ subprojects {
         compileOnly 'org.jspecify:jspecify:0.3.0'
         compileOnly 'io.github.eisop:checker-qual:3.34.0-eisop1'
         compileOnly 'io.github.eisop:checker-util:3.34.0-eisop1'
-        testCompileOnly 'io.github.eisop:checker-qual:3.34.0-eisop1'
-        checkerFramework 'io.github.eisop:checker:3.34.0-eisop1'
+        testCompileOnly 'io.github.eisop:checker-qual:3.34.0-eisop2'
+        checkerFramework 'io.github.eisop:checker:3.34.0-eisop2'
 
         testImplementation 'org.junit.jupiter:junit-jupiter-api:5.9.3'
         testImplementation 'org.junit.jupiter:junit-jupiter-params:5.9.3'
diff --git a/key.util/src/main/java/org/key_project/util/collection/DefaultImmutableSet.java b/key.util/src/main/java/org/key_project/util/collection/DefaultImmutableSet.java
index 70c0580ae60..ba1af27f3c9 100644
--- a/key.util/src/main/java/org/key_project/util/collection/DefaultImmutableSet.java
+++ b/key.util/src/main/java/org/key_project/util/collection/DefaultImmutableSet.java
@@ -3,9 +3,7 @@
  * SPDX-License-Identifier: GPL-2.0-only */
 package org.key_project.util.collection;
 
-import java.util.HashSet;
-import java.util.Iterator;
-import java.util.Set;
+import java.util.*;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
@@ -64,6 +62,10 @@ private DefaultImmutableSet(ImmutableList<T> elementList) {
         this.elementList = elementList;
     }
 
+    public static <T> ImmutableSet<T> fromCollection(Collection<T> seq) {
+        return new DefaultImmutableSet<>(ImmutableList.fromList(seq));
+    }
+
     // private static HashSet<String> previousComplains = new HashSet<>();
     private void complainAboutSize() {
         // // Immutable linear sets are very expensive with O(n) addition
diff --git a/settings.gradle b/settings.gradle
index b6b30a65546..fd11d70f3d6 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -16,4 +16,5 @@ include 'keyext.slicing'
 include 'keyext.caching'
 
 // ENABLE NULLNESS here or on the CLI
+// This flag is activated to enable the checker framework.
 // System.setProperty("ENABLE_NULLNESS", "true")
\ No newline at end of file