title: How to convert Map into javax.json.JsonObject?
body: <p>I can do so:</p>
  
  <pre><code>Map&lt;String, String&gt; mapA = ...;
  Map&lt;String, String&gt; mapB = mapA.entrySet().stream()
      .collect(Collectors.toMap(
          Map.Entry::getKey,
          Map.Entry::getValue
      ));
  </code></pre>
  
  <p>But when I'm trying to do this:</p>
  
  <pre><code>... mapA.entrySet().stream()
      .collect(JsonCollectors.toJsonObject(
          JsonObject.Entry::getKey,
          JsonObject.Entry::getValue
      ));
  </code></pre>
  
  <p>I get</p>
  
  <blockquote>
    <p>non-static method cannot be referenced from a static context</p>
  </blockquote>
  
  <p>for the <code>JsonObject.Entry::getKey, JsonObject.Entry::getValue</code> part.</p>
  
  <p>Why's that?</p>