Update package_manager_exists.sh

Author: CLHatch

.scripts/package_manager_exists.sh

@@ -7,7 +7,7 @@ package_manager_exists() {
 
     [[ -n ${PackageManager-} ]] || return 1
     run_script 'package_manager_is_valid' "${PackageManager}" || return 1
-    [[ -n $(command -v "${PM_PACKAGE_MANAGER_COMMAND["${PackageManager}"]}") ]] || return 1
+    [[ -n $(command -v "${PM_PACKAGE_MANAGER_COMMAND["${PackageManager}"]-}") ]] || return 1
 
     return 0
 }