fixed missing null check in ps handle

src/kernel/ps/ProcessHandle.hx

@@ -49,8 +49,10 @@ class ProcessHandle {
 	}
 
 	public function write(message: String): Void {
+		if (this.config.onWrite != null){
 			this.config.onWrite.invoke(message);
 		}
+	}
 
 	public function writeLine(message: String): Void {
 		this.write(message + "\n");