title: Add Interceptor from an existing OkHttpClient
body: <p>I have already built an instance of <code>OkHttpClient</code>. How do I add an interceptor to it? (I am also using Retrofit)</p>
  
  <p>I wish to add my authorization token to it. I currently get the following error:</p>
  
  <pre><code>Error creating evaluation class loader: com.intellij.debugger.engine.evaluation.EvaluateException: Method threw 'java.lang.NullPointerException' exception.
  java.lang.NullPointerException: parentLoader == null &amp;&amp; !nullAllowed
  </code></pre>
  
  <p>When I do:</p>
  
  <pre><code>okHttpClient = okHttpClient.newBuilder().addNetworkInterceptor(new Interceptor()
  {
      @Override
      public Response intercept(final Chain chain) throws IOException
      {
          final Request request = chain.request();
          Request newRequest;
  
          newRequest = request.newBuilder()
                              .addHeader(AUTHORIZATION_HEADER, String.format("Bearer %s", "Bob"))
                              .build();
          return chain.proceed(newRequest);
  
      }
  }).build();
  </code></pre>