code: public static ResolvableType forMethodReturnType(Method method, Class<?> implementationClass) {
          LettuceAssert.notNull(method, "Method must not be null");
          MethodParameter methodParameter = new MethodParameter(method, -1);
          methodParameter.setContainingClass(implementationClass);
          return forMethodParameter(methodParameter);
      }
docs: Return a {@link ResolvableType} for the specified {@link Method} return type. Use this variant when the class that
  declares the method includes generic parameter variables that are satisfied by the implementation class.
  
  @param method the source for the method return type
  @param implementationClass the implementation class
  @return a {@link ResolvableType} for the specified method return
  @see #forMethodReturnType(Method)