code: private FieldNode createFieldNodeCopy(String newName, ClassNode newType, FieldNode f) {
          if (newType == null)
              newType = f.getType();
          newType = newType.getPlainNodeReference();
  
          return new FieldNode(newName, f.getModifiers(), newType, f.getOwner(), f.getInitialValueExpression());
      }
docs: Creates a copy of a FieldNode with a new name and, optionally, a new type.
  
  @param newName The name for the new field node.
  @param newType The new type of the field.  If null, the old FieldNode's type will be used.
  @param f       The FieldNode to copy.
  @return The new FieldNode.