set myKMVar to my getKMVar("MY_KM_Variable")

on getKMVar(pKMVarNameStr)

  --- Compatible with Keyboard Maestro 6+ ---
  --     • Returns "" if variable is not found (just like KM 7 getvariable)
  
  tell application "Keyboard Maestro Engine"
    try
      set kmVar to value of variable pKMVarNameStr
      
    on error errMsg number errNum
      if (errNum = -1728) then
        --- KM Variable NOT Found ---
        set kmVar to ""
      else
        error errMsg
      end if
      -- END on error
      
    end try
  end tell
  
  return kmVar
  
end getKMVar