docs: private static Matcher<ExpressionTree> methodReceiverHasType(final Set<String> typeSet) {
      return new Matcher<ExpressionTree>() {
        @Override
        public boolean matches(ExpressionTree expressionTree, VisitorState state) {
          Type receiverType = ASTHelpers.getReceiverType(expressionTree);
          return typeSet.contains(receiverType.toString());
        }
      };
    }