Support running aliases.sh with "set -u"

python/LbEnv/data/aliases.sh

@@ -57,14 +57,14 @@ lb_set_workspace() {
 }
 alias lb-set-workspace=lb_set_workspace
 
-if [ -n "$BASH_VERSION" -a -n "$VIRTUAL_ENV" ] ; then
+if [ -n "${BASH_VERSION:-}" -a -n "${VIRTUAL_ENV:-}" ] ; then
   lb_enable_shell_completion() {
     source "$VIRTUAL_ENV/share/bash-completion/bash_completion"
   }
   alias lb-enable-shell-completion=lb_enable_shell_completion
 fi
 
-if [ -n "$ZSH_VERSION" -a -n "$VIRTUAL_ENV" ] ; then
+if [ -n "${ZSH_VERSION:-}" -a -n "${VIRTUAL_ENV:-}" ] ; then
   lb_enable_shell_completion() {
     source "$VIRTUAL_ENV/share/zsh/zsh_completion"
   }