title: Why AutoMapper nested mapping works without CreateMap for inner type
body: <p>Model to AutoMap:</p>
  
  <pre class="lang-cs prettyprint-override"><code>public class OuterSource
  {
      public int Value { get; set; }
      public InnerSource Inner { get; set; }
  }
  
  public class InnerSource
  {
      public int OtherValue { get; set; }
  }
  
  public class OuterDest
  {
      public int Value { get; set; }
      public InnerDest Inner { get; set; }
  }
  
  public class InnerDest
  {
      public int OtherValue { get; set; }
  }
  </code></pre>
  
  <p>I found that if I comment out <code>CreateMap</code> for inner type.
  Nested mapping still work. I would like to understand why it works, as it is not clearly stated in the documentation.</p>
  
  <pre class="lang-cs prettyprint-override"><code>var config = new MapperConfiguration(cfg =&gt; {
      cfg.CreateMap&lt;OuterSource, OuterDest&gt;();
      // cfg.CreateMap&lt;InnerSource, InnerDest&gt;();    // &lt;-- don't need this
  });
  config.AssertConfigurationIsValid();
  
  var source = new OuterSource
  {
      Value = 5,
      Inner = new InnerSource {OtherValue = 15}
  };
  var mapper = config.CreateMapper();
  var dest = mapper.Map&lt;OuterSource, OuterDest&gt;(source);
  </code></pre>
  
  <p>Note: I use AutoMapper version 8.1.0</p>