[type/__update_alternatives] Secure cdist-defined environment variables with :?

cdist/conf/type/__update_alternatives/explorer/alternatives

@@ -1,4 +1,4 @@
 #!/bin/sh -e
 
-update-alternatives --display "$__object_id" 2>/dev/null \
+update-alternatives --display "${__object_id:?}" 2>/dev/null \
     | awk -F ' - ' '/priority [0-9]+$/ { print $1 }'

cdist/conf/type/__update_alternatives/explorer/link

@@ -18,12 +18,12 @@ for altdir in \
     /var/lib/dpkg/alternatives \
     /var/lib/alternatives
 do
-    if [ ! -f "$altdir/$__object_id" ]
+    if [ ! -f "$altdir/${__object_id:?}" ]
     then
         continue
     fi
 
-    link="$( awk 'NR==2' "$altdir/$__object_id" )"
+    link="$( awk 'NR==2' "$altdir/${__object_id:?}" )"
 
     if [ -n "$link" ]
     then
@@ -33,7 +33,7 @@ done
 
 if [ -z "$link" ]
 then
-    echo "unable to get link for $__object_id" >&2
+    echo "unable to get link for ${__object_id:?}" >&2
     exit 1
 fi
 

cdist/conf/type/__update_alternatives/explorer/path_is

@@ -1,11 +1,11 @@
 #!/bin/sh -e
 
-path_is="$( update-alternatives --display "$__object_id" 2>/dev/null \
+path_is="$( update-alternatives --display "${__object_id:?}" 2>/dev/null \
     | awk '/link currently points to/ {print $5}' )"
 
 if [ -z "$path_is" ]
 then
-    echo "unable to get current path for $__object_id" >&2
+    echo "unable to get current path for ${__object_id:?}" >&2
     exit 1
 fi
 

cdist/conf/type/__update_alternatives/explorer/path_should_state

@@ -1,6 +1,6 @@
 #!/bin/sh -e
 
-if [ -f "$( cat "$__object/parameter/path" )" ]
+if [ -f "$( cat "${__object:?}/parameter/path" )" ]
 then
     echo 'present'
 else

cdist/conf/type/__update_alternatives/gencode-remote

@@ -18,26 +18,25 @@
 # You should have received a copy of the GNU General Public License
 # along with cdist. If not, see <http://www.gnu.org/licenses/>.
 
-path_is="$( cat "$__object/explorer/path_is" )"
+path_is="$( cat "${__object:?}/explorer/path_is" )"
 
-path_should="$( cat "$__object/parameter/path" )"
+path_should="$( cat "${__object:?}/parameter/path" )"
 
 if [ "$path_is" = "$path_should" ]
 then
     exit 0
 fi
 
-if [ "$( cat "$__object/explorer/path_should_state" )" = 'absent' ] && [ -z "$__cdist_dry_run" ]
+if [ "$( cat "${__object:?}/explorer/path_should_state" )" = 'absent' ] \
+    && [ -z "${__cdist_dry_run+dry run}" ]
 then
     echo "$path_should does not exist in target" >&2
     exit 1
 fi
 
-name="$__object_id"
+name=${__object_id:?}
 
-alternatives="$( cat "$__object/explorer/alternatives" )"
-
-if ! echo "$alternatives" | grep -Fxq "$path_should"
+if ! grep -Fxq "$path_should" "${__object:?}/explorer/alternatives"
 then
     if [ ! -f "$__object/parameter/install" ]
     then