title: mapping of non-iterable to iterable in mapstruct
body: <p>I am trying to map a non-iterable value i.e. String to a list of string using mapstruct.
  So I am using </p>
  
  <pre><code>@Mapping(target = "abc", expression = "java(java.util.Arrays.asList(x.getY().getXyz()))")
  </code></pre>
  
  <p>Here <code>abc</code> is <code>List&lt;String&gt;</code></p>
  
  <p><code>xyz</code> is a <code>String</code></p>
  
  <p>But for this i need to check for <code>null</code> explicitly.</p>
  
  <p>Is there any better way of maaping a non-iterable to iterable by converting non iterable to iterable.</p>