code: public TypeSerializer<UK> getKeySerializer() {
  		final TypeSerializer<Map<UK, UV>> rawSerializer = getSerializer();
  		if (!(rawSerializer instanceof MapSerializer)) {
  			throw new IllegalStateException("Unexpected serializer type.");
  		}
  
  		return ((MapSerializer<UK, UV>) rawSerializer).getKeySerializer();
  	}
docs: Gets the serializer for the keys in the state.
  
  @return The serializer for the keys in the state.