Adopt 'empty' as default value for shell vars, converted to JSON null is necessary

Author: bgandon

out

@@ -115,7 +115,7 @@ for channel in ${channels}; do
     if [[ "${always_notify}" != "true" && -z "${TEXT_FILE_CONTENT}" && -n "${text_file}" ]]; then
         text_interpolated=""
     else
-        if [[ "${attachments}" == "null" ]]; then
+        if [[ -z "${attachments}" ]]; then
             TEXT_FILE_CONTENT=${TEXT_FILE_CONTENT:-"_(no notification provided)_"}
         fi
 
@@ -124,7 +124,7 @@ for channel in ${channels}; do
         if [[ -z "${text_interpolated}" ]]; then
             text_interpolated="_(missing notification text)_"
             if [[ -n "${attachments}" ]]; then
-                text_interpolated="null"
+                text_interpolated=""
             fi
         fi
 
@@ -138,18 +138,18 @@ for channel in ${channels}; do
                 --arg     "text_interpolated" "${text_interpolated}" \
                 --arg     "username"          "${username}" \
                 --argjson "link_names"        "${link_names}" \
-                --arg "icon_url"          "${icon_url}" \
-                --arg "icon_emoji"        "${icon_emoji}" \
-                --arg "channel"           "${channel}" \
-                --arg "attachments"       "${attachments}" \
+                --arg     "icon_url"          "${icon_url}" \
+                --arg     "icon_emoji"        "${icon_emoji}" \
+                --arg     "channel"           "${channel}" \
+                --arg     "attachments"       "${attachments}" \
                 '{
-                    text:        $text_interpolated,
-                    username:    $username    // null,
+                    text:        $text_interpolated // null,
+                    username:    $username          // null,
                     link_names:  $link_names,
-                    icon_url:    $icon_url    // null,
-                    icon_emoji:  $icon_emoji  // null,
-                    channel:     $channel     // null,
-                    attachments: $attachments // null
+                    icon_url:    $icon_url          // null,
+                    icon_emoji:  $icon_emoji        // null,
+                    channel:     $channel           // null,
+                    attachments: $attachments       // null
                 }'
         )