Fix test for defaultValue for AdditionalProperties fields when using generateAliasAsModel

Author: jpfinne

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/AbstractJavaCodegenTest.java

@@ -552,7 +552,7 @@ public void toDefaultValueTest() {
 
         ModelUtils.setGenerateAliasAsModel(true);
         defaultValue = codegen.toDefaultValue(codegen.fromProperty("", schema), schema);
-        Assert.assertEquals(defaultValue, "new HashMap<>()");
+        Assert.assertNull(defaultValue);
 
         // Test default value for date format
         DateSchema dateSchema = new DateSchema();