How to use Gson for mixed types?

I am trying to figure out how to parse a json string via Gson.  I have a json string (examples below) that can return mixed types into an EmailSubscriber object.  The "merges" field can have just a {string:string, string:string} pattern, OR in certain cases, one of the "strings" is actually a Grouping object.  I have included the two very simplified examples below.  

How can I tell the gson parser to handle the possibility of this extra array object?

Example parsing classes

class EmailSubscriber {
	String status;
                // How can this handle mixed types??
	HashMap<String, String> merges;
                // Getters & setters below...
}
class Grouping {
	String id;
	String name;
	String groups;
	// Getters and setters below...	
}

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Example Json reponses

// Works
json: {"status":"subscribed","merges":{"EMAIL":"test@gmail.com","FNAME":"Burton","LNAME":"Rhodes","DROPDWN":"Eggs"}}

// Doesn't work with introduced sub array (grouping)
json: {"status":"subscribed","merges":{"EMAIL":"test@gmail.com","FNAME":"Burton","LNAME":"Rhodes","DROPDWN":"Eggs","GROUPINGS":[{"id":4809,"name":"MyGrouping","groups":"Group1, Group2"}]}}

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Example parsing code

Gson gson = new Gson();
JsonParser parser = new JsonParser();
JsonObject jsonObject = parser.parse(responseBody).getAsJsonObject();
EmailSubscriber emailSubscriber = gson.fromJson(jsonObject, EmailSubscriber.class);

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I tried changing merges to "HashMap<String, Object> merges", but json gives me a the error "com.google.gson.JsonParseException: Type information is unavailable, and the target is not a primitive: [{"id":4809,"name":"MyGrouping","groups":"Group1, Group2"}]"

I am at a loss in how to program the json parser to successfully deserialize this type of "variable" json feed.  Any suggestions?