light elements should not be simplified especially when they were not changed (EA-47908 - IOE: CheckUtil.checkWritable)

java/java-analysis-impl/src/com/intellij/codeInsight/daemon/impl/quickfix/ExtendsListFix.java

@@ -172,6 +172,12 @@ public class ExtendsListFix extends LocalQuickFixAndIntentionActionOnPsiElement
       }
       list = (PsiReferenceList) element.getParent();
     }
+
+    //nothing was changed
+    if (!add && !alreadyExtends) {
+      return list;
+    }
+    
     return (PsiReferenceList)JavaCodeStyleManager.getInstance(extendsList.getProject()).shortenClassReferences(list);
   }
 }

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/changeExtendsToImplements/afterTypeParameter.java

@@ -0,0 +1,4 @@
+// "Make 'K' implement 'java.lang.Runnable'" "true"
+
+interface RemoteStore<K extends Runnable, V>{}
+class BackedRemoteStore<K extends Runnable, V> implements RemoteStore<K, V> {}

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/quickFix/changeExtendsToImplements/beforeTypeParameter.java

@@ -0,0 +1,4 @@
+// "Make 'K' implement 'java.lang.Runnable'" "true"
+
+interface RemoteStore<K extends Runnable, V>{}
+class BackedRemoteStore<K, V> implements RemoteStore<<caret>K, V> {}