code: public String createMethodTypeSignature(ExecutableElement method) {
      if (!hasGenericSignature(method)) {
        return null;
      }
      StringBuilder sb = new StringBuilder();
      genMethodTypeSignature(method, sb);
      return sb.toString();
    }
docs: Create a method signature string for a specified method or constructor.
  
  @return the signature if method is generic or use type variables, else null.