Why would JOCL CL.clEnqueueReadBuffer never return?

Question

Currently I have a kernel that is supposed to take a flattened array of bytes and transform render some image, I have all of this implemented, however, I have a line of code that never returns

ret = CL.clEnqueueReadBuffer(this.commandQueue, this.finalImageBuffer, CL.CL_TRUE, 0, this.outputSize, Pointer.to(this.outArray), 0, null, null);

why would it never return, that's my question.

Thanks in advance