This batch script terminates when %CHECKCONTINUE% is given a null value by not inputting anything on line 13 (SET /p CHECKCONTINUE=Okay to continue? (y/n):), why is this?

@ECHO OFF
SETLOCAL
TITLE Registry restore script
REM Restores registry settings and disables the cloud

SET %CHECKCONTINUE%=

:listaction
ECHO I'm about to...
ECHO 1.) Remove the registry data that specifies settings for TF2
ECHO 2.) Forcibly disable Steam Cloud.
ECHO.
SET /p CHECKCONTINUE=Okay to continue? (y/n): 

REM No?
IF %CHECKCONTINUE%==n GOTO exit
IF %CHECKCONTINUE%==no GOTO exit

REM Yes?
IF %CHECKCONTINUE%==y GOTO start
IF %CHECKCONTINUE%==yes GOTO start

REM Did they put something else?
IF DEFINED %CHECKCONTINUE% GOTO loop-notvalid

REM Did they not put anything at all?
IF NOT DEFINED %CHECKCONTINUE% GOTO loop-noreply

:start
REM Delete application specific data
REG DELETE HKEY_CURRENT_USER\Software\Valve\Source\tf\Settings /f
REG DELETE HKEY_CURRENT_USER\Software\Valve\Steam\Apps\440 /f

REM Disable Steam Cloud for TF2
REG ADD HKEY_CURRENT_USER\Software\Valve\Steam\Apps\440 /v Cloud /t REG_DWORD /d "0x0" /f

:exit
ENDLOCAL
EXIT

:loop-notvalid
ECHO.
ECHO That's not a valid reply. Try again.
ECHO.
SET %CHECKCONTINUE%=
GOTO listaction

:loop-noreply
ECHO.
ECHO You must enter a reply.
ECHO.
SET %CHECKCONTINUE%=
GOTO listaction