bash unbound variable

Errors like this:

 "$NOTHING_HERE": unbound variable

Come up when bash is run with unset variables disallowed.

# Allow unset variables in a script
set -o unset

# Disallow unset variables in a script
set -o nounset

# Run a script with unset variables disallowed
bash -u /path/to/script

See The Set Builtin (Bash Reference Manual)