You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: openAIMessages.m
    path of file: ./repos/llms-with-matlab
    
    the code of the file until where you have to start completion: classdef (Sealed) openAIMessages   
    %openAIMessages - Create an object to manage and store messages in a
    
function this = addUserMessage(this, content)
            %addUserMessage   Add user message.
            %
            %   MESSAGES = addUserMessage(MESSAGES, CONTENT) adds a user message
            %   with the specified content to MESSAGES. CONTENT must be a text scalar.
            %
            %   Example:
            %   % Create messages object
            %   messages = openAIMessages;
            %
            %   % Add user message
            %   messages = addUserMessage(messages, "Where is Natick located?");

            arguments
                this (1,1) openAIMessages
                content {mustBeNonzeroLengthTextScalar}
            end