code: public static ResolvableType forMethodReturnType(Method method) {
  		Assert.notNull(method, "Method must not be null");
  		return forMethodParameter(MethodParameter.forMethodOrConstructor(method, -1));
  	}
docs: Return a {@link ResolvableType} for the specified {@link Method} return type.
  @param method the source for the method return type
  @return a {@link ResolvableType} for the specified method return
  @see #forMethodReturnType(Method, Class)