diff --git a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/ClassScope.java b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/ClassScope.java
index 2f107d598b..e58b8ee002 100644
--- a/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/ClassScope.java
+++ b/pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/ClassScope.java
@@ -307,6 +307,9 @@ public class ClassScope extends AbstractJavaScope {
     }
 
     private String qualifyTypeName(String typeImage) {
+        if (typeImage == null) {
+            return null;
+        }
         for (String qualified : this.getEnclosingScope(SourceFileScope.class).getQualifiedTypeNames().keySet()) {
             int fullLength = qualified.length();
             int nameLength = typeImage.length();
diff --git a/pmd-java/src/test/java/net/sourceforge/pmd/lang/java/symboltable/ClassScopeTest.java b/pmd-java/src/test/java/net/sourceforge/pmd/lang/java/symboltable/ClassScopeTest.java
index f3f1443198..df2e904057 100644
--- a/pmd-java/src/test/java/net/sourceforge/pmd/lang/java/symboltable/ClassScopeTest.java
+++ b/pmd-java/src/test/java/net/sourceforge/pmd/lang/java/symboltable/ClassScopeTest.java
@@ -269,6 +269,11 @@ public class ClassScopeTest extends STBBaseTst {
     	
     }
 
+    @Test
+    public void testNullType() {
+        parseCode(TEST_NULL_TYPE);
+    }
+
     private static final String NESTED_CLASS_FIELD_AND_PARAM =
             "public class Foo {" + PMD.EOL +
             " class Test {" + PMD.EOL +
@@ -376,6 +381,12 @@ public class ClassScopeTest extends STBBaseTst {
             " }" + PMD.EOL +
             "}";
 
+    public static final String TEST_NULL_TYPE =
+            "public abstract class NullTypeTest {" + PMD.EOL +
+            "   protected Comparator<TreeNode> nodesComparator = (o1, o2) -> StringHelper.saveCompare(getFilterableString(o1), getFilterableString(o2));" + PMD.EOL +
+            "   public abstract String getFilterableString(TreeNode node);" + PMD.EOL +
+            "}";
+
     public static junit.framework.Test suite() {
         return new junit.framework.JUnit4TestAdapter(ClassScopeTest.class);
     }