diff --git a/base-test/org.eclipse.jdt.groovy.core.tests.compiler/src/org/eclipse/jdt/groovy/core/tests/basic/GroovySimpleTests.java b/base-test/org.eclipse.jdt.groovy.core.tests.compiler/src/org/eclipse/jdt/groovy/core/tests/basic/GroovySimpleTests.java
index 16752d950b..3f6f3ecccc 100644
--- a/base-test/org.eclipse.jdt.groovy.core.tests.compiler/src/org/eclipse/jdt/groovy/core/tests/basic/GroovySimpleTests.java
+++ b/base-test/org.eclipse.jdt.groovy.core.tests.compiler/src/org/eclipse/jdt/groovy/core/tests/basic/GroovySimpleTests.java
@@ -24,9 +24,11 @@
 import static org.junit.Assume.assumeTrue;
 
 import java.io.File;
+import java.util.Collections;
 import java.util.Iterator;
 import java.util.Map;
 
+import org.codehaus.groovy.control.CompilerConfiguration;
 import org.codehaus.jdt.groovy.internal.compiler.ast.EventListener;
 import org.codehaus.jdt.groovy.internal.compiler.ast.GroovyClassScope;
 import org.codehaus.jdt.groovy.internal.compiler.ast.GroovyCompilationUnitDeclaration;
@@ -3243,6 +3245,62 @@ public void testImplementingInterface_MethodWithParameters3_JextendsG() {
         runConformTest(sources, "success");
     }
 
+    @Test
+    public void testCallingJavaFromGroovy1() {
+        //@formatter:off
+        String[] sources = {
+            "p/Main.groovy",
+            "package p\n" +
+            "class Main {\n" +
+            "  static main(args) {\n" +
+            "    new J().run()\n" +
+            "    print new J().name\n" +
+            "  }\n" +
+            "}\n",
+
+            "p/J.java",
+            "package p;\n" +
+            "public class J {\n" +
+            "  public String name = \"name\";\n" +
+            "  public void run() { System.out.print(\"success\"); }\n" +
+            "}\n",
+        };
+        //@formatter:on
+
+        runConformTest(sources, "successname");
+    }
+
+    @Test
+    public void testCallingJavaFromGroovy2() {
+        //@formatter:off
+        String[] sources = {
+            "p/Main.groovy",
+            "package p\n" +
+            "@Tag(value=4)\n" +
+            "class Main {\n" +
+            "  static main(args) {\n" +
+            "    new J().run()\n" +
+            "  }\n" +
+            "}\n",
+
+            "p/J.java",
+            "package p;\n" +
+            "public class J {\n" +
+            "  public String name = \"name\";\n" +
+            "  public void run() { System.out.print(\"success\"); }\n" +
+            "}\n",
+
+            "p/Tag.java",
+            "package p;\n" +
+            "public @interface Tag {\n" +
+            "  int value() default 3;\n" +
+            "}\n",
+        };
+        //@formatter:on
+
+        runConformTest(sources, "success");
+    }
+
     @Test
     public void testCallingMethods_JcallingG() {
         //@formatter:off
@@ -4270,62 +4328,6 @@ public void testClashingMethodsWithDefaultParams() {
             "----------\n");
     }
 
-    @Test
-    public void testCallingJavaFromGroovy1() throws Exception {
-        //@formatter:off
-        String[] sources = {
-            "p/Code.groovy",
-            "package p;\n" +
-            "class Code {\n" +
-            "  public static void main(String[] argv) {\n" +
-            "    new J().run();\n" +
-            "    print new J().name;\n" +
-            "  }\n" +
-            "}\n",
-
-            "p/J.java",
-            "package p;\n" +
-            "public class J {\n" +
-            "  public String name = \"name\";\n" +
-            "  public void run() { System.out.print(\"success\"); }\n" +
-            "}\n",
-        };
-        //@formatter:on
-
-        runConformTest(sources, "successname");
-    }
-
-    @Test
-    public void testCallingJavaFromGroovy2() throws Exception {
-        //@formatter:off
-        String[] sources = {
-            "p/Code.groovy",
-            "package p;\n" +
-            "@Wibble(value=4)\n" +
-            "class Code {\n" +
-            "  public static void main(String[] argv) {\n" +
-            "    new J().run();\n" +
-            "  }\n" +
-            "}\n",
-
-            "p/J.java",
-            "package p;\n" +
-            "public class J {\n" +
-            "  public String name = \"name\";\n" +
-            "  public void run() { System.out.print(\"success\"); }\n" +
-            "}\n",
-
-            "p/Wibble.java",
-            "package p;\n" +
-            "public @interface Wibble {\n" +
-            "  int value() default 3;\n" +
-            "}\n",
-        };
-        //@formatter:on
-
-        runConformTest(sources, "success");
-    }
-
     @Test
     public void testTypeVariableBoundIsRawType() {
         //@formatter:off
@@ -4609,6 +4611,16 @@ public void testScriptCallJava() {
         runConformTest(sources, "abc");
     }
 
+    @Test
+    public void testConfigDefaults() {
+        CompilerConfiguration cc = CompilerConfiguration.DEFAULT;
+        assertEquals(Collections.emptyList(), cc.getClasspath());
+        assertEquals(Collections.emptyList(), cc.getCompilationCustomizers());
+        assertEquals(Collections.emptyMap(), cc.getJointCompilationOptions());
+        assertEquals(Collections.singleton("groovy"), cc.getScriptExtensions());
+        assertEquals(Collections.emptySet(), cc.getDisabledGlobalASTTransformations());
+    }
+
     @Test
     public void testConfigScriptWithError() {
         Map<String, String> options = getCompilerOptions();
diff --git a/base/org.codehaus.groovy24/src/org/codehaus/groovy/control/CompilerConfiguration.java b/base/org.codehaus.groovy24/src/org/codehaus/groovy/control/CompilerConfiguration.java
index 4e54513466..ba6b5386a7 100644
--- a/base/org.codehaus.groovy24/src/org/codehaus/groovy/control/CompilerConfiguration.java
+++ b/base/org.codehaus.groovy24/src/org/codehaus/groovy/control/CompilerConfiguration.java
@@ -82,7 +82,7 @@ public class CompilerConfiguration {
     public static final CompilerConfiguration DEFAULT = new CompilerConfiguration() {
         @Override
         public List<String> getClasspath() {
-            return Optional.ofNullable(super.getClasspath()).map(Collections::unmodifiableList).orElse(null);
+            return Collections.unmodifiableList(super.getClasspath());
         }
         @Override
         public List<CompilationCustomizer> getCompilationCustomizers() {
@@ -90,19 +90,19 @@ public List<CompilationCustomizer> getCompilationCustomizers() {
         }
         @Override
         public Set<String> getDisabledGlobalASTTransformations() {
-            return Optional.ofNullable(super.getDisabledGlobalASTTransformations()).map(Collections::unmodifiableSet).orElse(null);
+            return Optional.ofNullable(super.getDisabledGlobalASTTransformations()).map(Collections::unmodifiableSet).orElse(Collections.emptySet());
         }
         @Override
         public Map<String, Object> getJointCompilationOptions() {
-            return Optional.ofNullable(super.getJointCompilationOptions()).map(Collections::unmodifiableMap).orElse(null);
+            return Optional.ofNullable(super.getJointCompilationOptions()).map(Collections::unmodifiableMap).orElse(Collections.emptyMap());
         }
         @Override
         public Map<String, Boolean> getOptimizationOptions() {
-            return Optional.ofNullable(super.getOptimizationOptions()).map(Collections::unmodifiableMap).orElse(null);
+            return Collections.unmodifiableMap(super.getOptimizationOptions());
         }
         @Override
         public Set<String> getScriptExtensions() {
-            return Optional.ofNullable(super.getScriptExtensions()).map(Collections::unmodifiableSet).orElse(null);
+            return Collections.unmodifiableSet(super.getScriptExtensions());
         }
 
         @Override
diff --git a/base/org.codehaus.groovy25/src/org/codehaus/groovy/control/CompilerConfiguration.java b/base/org.codehaus.groovy25/src/org/codehaus/groovy/control/CompilerConfiguration.java
index 2022eab294..9b709720a4 100644
--- a/base/org.codehaus.groovy25/src/org/codehaus/groovy/control/CompilerConfiguration.java
+++ b/base/org.codehaus.groovy25/src/org/codehaus/groovy/control/CompilerConfiguration.java
@@ -139,12 +139,12 @@ public List<CompilationCustomizer> getCompilationCustomizers() {
 
         @Override
         public Set<String> getDisabledGlobalASTTransformations() {
-            return Collections.emptySet();
+            return Optional.ofNullable(super.getDisabledGlobalASTTransformations()).map(Collections::unmodifiableSet).orElse(Collections.emptySet());
         }
 
         @Override
         public Map<String, Object> getJointCompilationOptions() {
-            return Collections.unmodifiableMap(super.getJointCompilationOptions());
+            return Optional.ofNullable(super.getJointCompilationOptions()).map(Collections::unmodifiableMap).orElse(Collections.emptyMap());
         }
 
         @Override