ive implemented getopt for the command line but have this problem,

Code:

#!/bin/sh
text=""
set -- getopt "t" etc ....    #sets arguments
while :
do
   case "$1" in                  #gets arguments
   -t: shift; text="$1" ;;
   shift
done
shift

if [ $text = "" ]
then
   echo "no text"
else
   echo "text"
fi

when i run the program ./script -t <text>
it prints "text"
but when i just run ./script
it returns a "arguments expected" message, (shouldnt it return "no text" ?)
is there a way to fix this, i want to be able to run ./script without it complaining as well as ./script -t <text>