An easier, less ugly way to do this is at the shell level, honestly.
Now, what if we don’t want to empty the trash, but we want to clear out “~/Documents”? Note that this doesn’t take prisoners, so it may be worthwhile to add a confirmation dialog, depending on your use!
do shell script "/bin/ls $HOME/Documents/"
-- we run the above ls command so if our string is BAD, or something else goes wrong while looking for ~/Documents, the script breaks HERE instead of the next shell command.
-- we don't ls with * so we don't nuke script performance.
do shell script "/bin/rm -rf $HOME/Documents/*"
on error theError
-- the alert is optional, but the try/on error is NOT OPTIONAL!
display alert "There was a problem removing the contents of the Documents folder." as critical message theError