static protected FieldNode addLegacyMixinFieldIfNonExistent(ClassNode classNode, ClassNode fieldType, String fieldName) {
ClassNode targetAwareInterface = GrailsASTUtils.findInterface(fieldType, new ClassNode(TestMixinTargetAware.class).getPlainNodeReference());
if (classNode != null && classNode.getField(fieldName) == null) {
Expression constructorArgument = new ArgumentListExpression();
if(targetAwareInterface != null) {
MapExpression namedArguments = new MapExpression();
namedArguments.addMapEntryExpression(new MapEntryExpression(new ConstantExpression("target"), new VariableExpression("this")));
constructorArgument = namedArguments;
}