Empty string is a file? ( if [ ! -f "" ] )

The script is called **isFile.sh** and looks like this:

#!/bin/sh

echo $1
echo $2

if [ ! -f $1 ]; then
  echo "$1 (arg1) is not a file"
fi

if [ ! -f $2 ]; then
  echo "$2 (arg2) is not a file"
fi

First I created a file by doing touch file.exist. And I ran bash isFile.sh file.exist file.notexist The output was: >file.exist > >file.notexist > >file.notexist (arg2) is not a file ---------------------------------------------------- Then I ran bash isFile.sh "" file.notexist The output was: >(# empty line) > >file.notexist > >file.notexist (arg2) is not a file Expected output is: >(# empty line) > >file.notexist > >(arg1) is not a file > >file.notexist (arg2) is not a file Can somebody explain why?