diff --git a/featlib/curl.sh b/featlib/curl.sh
index 8c71d9b..fcb5a50 100755
--- a/featlib/curl.sh
+++ b/featlib/curl.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1604316819}" ] && return; GREZZO_1604316819=0
+[ -n "${GREZZO_1604316819-}" ] && return; GREZZO_1604316819=0
 
 function feat_addpacks_curl() {
     if ! feat_missing "apt-get"; then
diff --git a/featlib/docker.sh b/featlib/docker.sh
index f21c22c..05b083a 100755
--- a/featlib/docker.sh
+++ b/featlib/docker.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1577141523}" ] && return; GREZZO_1577141523=0
+[ -n "${GREZZO_1577141523-}" ] && return; GREZZO_1577141523=0
 
 . "$(this_script_path)/lsb-release.sh"
 
diff --git a/featlib/lsb-release.sh b/featlib/lsb-release.sh
index 445f1ee..416cfa3 100644
--- a/featlib/lsb-release.sh
+++ b/featlib/lsb-release.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1737747200}" ] && return; GREZZO_1737747200=0
+[ -n "${GREZZO_1737747200-}" ] && return; GREZZO_1737747200=0
 
 function feat_add_lsb_release() {
 	if ! feat_missing "apt-get"; then
diff --git a/featlib/npm.sh b/featlib/npm.sh
index 919687c..5d95c06 100755
--- a/featlib/npm.sh
+++ b/featlib/npm.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1577142009}" ] && return; GREZZO_1577142009=0
+[ -n "${GREZZO_1577142009-}" ] && return; GREZZO_1577142009=0
 
 function feat_addpacks_npm_dev() {
     if ! feat_missing "apt-get"; then
diff --git a/featlib/pip.sh b/featlib/pip.sh
index d9cca39..58abba1 100755
--- a/featlib/pip.sh
+++ b/featlib/pip.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1577142035}" ] && return; GREZZO_1577142035=0
+[ -n "${GREZZO_1577142035-}" ] && return; GREZZO_1577142035=0
 
 . "$(this_script_path)/curl.sh"
 
diff --git a/featlib/poetry.sh b/featlib/poetry.sh
index 8aea138..3afaabd 100644
--- a/featlib/poetry.sh
+++ b/featlib/poetry.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1577142078}" ] && return; GREZZO_1577142078=0
+[ -n "${GREZZO_1577142078-}" ] && return; GREZZO_1577142078=0
 
 . "$(this_script_path)/pip.sh"
 . "$(this_script_path)/curl.sh"
diff --git a/featlib/poetry/django.sh b/featlib/poetry/django.sh
index 1c1defe..5d9e813 100755
--- a/featlib/poetry/django.sh
+++ b/featlib/poetry/django.sh
@@ -3,7 +3,7 @@
 # Questo è un esempio di custom callback. poetry_feat_needed chiama prima poetry_feat_add_django,
 # qui definito, che può effettuare altre operazioni prima e/o dopo il lancio di poetry_feat_add.
 
-[ ! -z "${GREZZO_1577141483}" ] && return; GREZZO_1577141483=0
+[ -n "${GREZZO_1577141483-}" ] && return; GREZZO_1577141483=0
 unset CDPATH
 DOVE="$(cd "$(dirname "$(readlink -f -- "${BASH_SOURCE[0]}")")" > /dev/null && pwd -P)"
 
diff --git a/featlib/rustup.sh b/featlib/rustup.sh
index 4427a81..6abb168 100755
--- a/featlib/rustup.sh
+++ b/featlib/rustup.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_1604315952}" ] && return; GREZZO_1604315952=0
+[ -n "${GREZZO_1604315952-}" ] && return; GREZZO_1604315952=0
 
 . "$(this_script_path)/curl.sh"
 
diff --git a/grezzo.sh b/grezzo.sh
index acdeeb7..d872f4f 100755
--- a/grezzo.sh
+++ b/grezzo.sh
@@ -1,5 +1,5 @@
 #! /bin/bash --
-[ ! -z "${GREZZO_MAIN}" ] && return; GREZZO_MAIN=0
+[ -n "${GREZZO_MAIN-}" ] && return; GREZZO_MAIN=0
 
 export DEBIAN_FRONTEND=noninteractive
 export DEBCONF_NONINTERACTIVE_SEEN=true