Simulink TCP Sender and Receiver module for String

I am trying to use Simulink's TCP sender and receiver modules to send and receive String data types. I'm already able to send double values as seen in the figure below. But the problem is how to send String values, and if that is possible. The strange part is when I define the TCP echo server inside Matlab itself, then the current sample works. But when I defined the TCP echo server outside of Matlab (I created a Java server). The Java server does not receive anything; it shows null, and thus nothing shows up in the scope. Any clues on what is going on?