DMS Support for mapping rules - dynamodb-map data type

I am trying to migrate data from Oracle DB to DynamoDB. In one of the column, I have a JSON as a string value which should be stored as Map (document) in DynamoDB. When I try to migrate using the DMS, the value is always migrated as a string and not a map. I have used the mapping rules for transformation and it adds an empty map when I define the target data type as Map.

{
            "target-attribute-name": "myJSONValue",
            "attribute-type": "document",
            "attribute-sub-type": "dynamodb-map",
            "value": {
              "M": "${myJSONValue}"
            }
 }

I am aware that DMS is not supporting the Map data type, but is there any other way I can do this mapping?