title: Handle optional JSON field in HTTP request body
body: <p>I have a struct like this:</p>
  
  <pre><code>type MyStruct struct {
      Name  string `json:"name"`
      Age   int    `json:"age"`
      Email string `json:"email"`
  } 
  </code></pre>
  
  <p>Then I have some value (could be default, which means I do not need to update this value) to feed in as HTTP request data.  I noticed the generated JSON body will always contains all three fields (<code>name</code>, <code>age</code> and <code>email</code>), even if I don't need to update all of them. Like this:</p>
  
  <pre><code>{
    "name":"Kevin",
    "age":10,
    "email":""
  }
  </code></pre>
  
  <p>Is there a way to Marshal so that the JSON body contains not all fields with the same struct?  Example:</p>
  
  <pre><code>{
    "name":"kevin"
  }
  </code></pre>