title: Json serialization of a simple map is causing stackOverflowErrors
body: <p>This simple code:</p>
  
  <pre><code>public static void Test() throws JsonProcessingException {
      Map&lt;Object, Object&gt; request = new HashMap&lt;&gt;();
      request.put("id", "test_0001");
      request.put("version", 1);
  
      Map&lt;Object, Object&gt; fields = new HashMap&lt;&gt;();
      fields.put("uri", "blah/blah");
      fields.put("owner", "me");
  
      request.put("fields", request);
  
      ObjectMapper om = new ObjectMapper();
      System.out.println(om.writeValueAsString(request));
  }
  </code></pre>
  
  <p>Is causing this exception:</p>
  
  <pre><code>Exception in thread "main" java.lang.StackOverflowError
      at java.lang.Enum.ordinal(Enum.java:103)
      at com.fasterxml.jackson.databind.MapperFeature.getMask(MapperFeature.java:259)
      at com.fasterxml.jackson.databind.cfg.MapperConfig.isEnabled(MapperConfig.java:110)
      at com.fasterxml.jackson.databind.SerializationConfig.getAnnotationIntrospector(SerializationConfig.java:404)
      at com.fasterxml.jackson.databind.SerializerProvider.getAnnotationIntrospector(SerializerProvider.java:307)
      at com.fasterxml.jackson.databind.ser.std.MapSerializer.createContextual(MapSerializer.java:235)
      at com.fasterxml.jackson.databind.SerializerProvider._handleContextual(SerializerProvider.java:968)
      at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:447)
      at com.fasterxml.jackson.databind.ser.impl.PropertySerializerMap.findAndAddSerializer(PropertySerializerMap.java:38)
      at com.fasterxml.jackson.databind.ser.std.MapSerializer._findAndAddDynamic(MapSerializer.java:516)
      at com.fasterxml.jackson.databind.ser.std.MapSerializer.serializeFields(MapSerializer.java:386)
      at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:312)
      at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:26)
  etc...
  </code></pre>
  
  <p>And for the life of me I cant figure out why. All I have found with by searching is people having issues because of recursive references, but that's not the case in this instance.</p>