title: GraphQL java: Throwing exceptions when request has unused variables
body: <p>Let's say I have a request payload with a variables map and a query. Does <code>graphql-java</code> have any out-of-the-box mechanisms that I can use to detect unused variables in the payload? </p>
  
  <p>For example: </p>
  
  <pre><code>type Query { hello : String! } # this just resolves to "hello world"
  </code></pre>
  
  <p>When the user sends in <code>{foo: 42}</code> as the <code>variables</code> in the request payload, I want to throw an error (say<code>IllegalArgumentException</code>).</p>
  
  <p>Edit: Answers/comments on how to implement this without any out-of-the-box mechanisms are also welcome.</p>