title: Why checkNotNull() is not annotated with @Nonnull
body: <p>I found inconvenient that <code>checkNotNull()</code> precondition in guava is not marked with <code>@Nonull</code> annotation. Consider following example:</p>
  
  <pre><code>State(Set&lt;Model&gt; models, Set&lt;Variation&gt; variations) {
    this.models = checkNotNull(models);
    this.variations = checkNotNull(variations);
  
    if (this.variations == null) {
       throw new IllegalArgumentException();
    }
    this.engine = createEngine();
  }
  </code></pre>
  
  <p>So IDE could not found that <code>variations == null</code> is always false. Is there any particular reasons why this precondition is not marked with <code>@Nonull</code> (even if it's arguments are defined using <code>@Nullable</code>).</p>