problem: I can't display the player who executed the command in the message sent to the player Java Forge mod

I send a warn message to the player in command 

my command input: /warn <player> <reason of warn>

exemple:

Tiwo68's tchat (I execute this): /warn player1 spam

player1 tchat: (he see this): You have been warned by tiwo68

output:

You have been warned by tiwo68

I send a message to the player1 in this exemple

problem: I can't display the player who executed the command >:(

could someone help me?