title: ObjectMapper throwing JsonMappingException for the attribute not present in the JSON string on deserialization
body: <p>I am using the Jackson ObjectMapper to serialize and deserialize a Java object. Even if the input JSON string does not have the specific attribute it's throwing an exception:</p>
  <blockquote>
  <p>com.fasterxml.jackson.databind.JsonMappingException: Can not find a
  (Map) Key deserializer for type [simple type]</p>
  </blockquote>
  <p>Suppose below is the class</p>
  <pre class="lang-java prettyprint-override"><code>public class Employee {
  
      private HashMap&lt;Key,String&gt; map = null;
      
      private String firstName;
      
      // getter &amp;&amp; setters
  }
  </code></pre>
  <p>I understand that I have to write the custom deserializer for the map attribute but even if I am not sending this in the
  JSON string &quot;{&quot;firstName&quot;:&quot;AVD&quot;}&quot;, why getting this error? If this is the Jackson default implementation for deserialization
  can we change the behavior?</p>