Quote ruby interpolated data in bash commands

Bash conditionals demonstrate strange behaviors when not given an arg.
Given the following:

    if [ -f  ]; then
      echo "how did I get here?"
    fi
    #=> how did I get here?

Wrapping ruby interpolated variables in quotes act as expected:

    if [ -f '' ]; then echo
      "how did I get here?"
    else
      echo "the empty string is not a file"
    fi
    #=> the empty string is not a file

The moral of the story is that bash exists to make everybody sad.