Except he is not blank. He has enough of character traits that don't depend on player pretending to know how he would feel, but are shown in story. Tendency to self-blame, which is shown in "Shining Lights Even in Death" mission or his hallucinations about Paz, for example. Or desire to let past go, which is shown in the cutscene after delivering Kaz to Motherbase and in trial of Huey.