title: Putting null value into HashMap is not possible somehow
body: <p>I'm writing an Android application and use <code>HashMap&lt;String,MyClass&gt;</code>. According to Java and Android documentation the HashMap should accept both null keys and values. But, strangely, I can't put null value into my map. In the code:</p>
  
  <pre><code>myMap.put(1, null);
  </code></pre>
  
  <p>I'm getting the error:</p>
  
  <p><code>The method put(String, MyClass) in the type HashMap&lt;String,MyClass&gt; is not applicable for the arguments (int, null)</code>.</p>
  
  <p>Why is that? What can be wrong and how to fix?</p>