Allow blank strings to be used for env var property substitutions

Fixes #4663

packages/node_modules/@node-red/editor-client/locales/en-US/editor.json

@@ -643,6 +643,7 @@
             "errors": {
                 "catalogLoadFailed": "<p>Failed to load node catalogue.</p><p>Check the browser console for more information</p>",
                 "installFailed": "<p>Failed to install: __module__</p><p>__message__</p><p>Check the log for more information</p>",
+                "installTimeout": "<p>Install continuing the background.</p><p>Nodes will appear in palette when complete. Check the log for more information.</p>",
                 "removeFailed": "<p>Failed to remove: __module__</p><p>__message__</p><p>Check the log for more information</p>",
                 "updateFailed": "<p>Failed to update: __module__</p><p>__message__</p><p>Check the log for more information</p>",
                 "enableFailed": "<p>Failed to enable: __module__</p><p>__message__</p><p>Check the log for more information</p>",

packages/node_modules/@node-red/editor-client/src/js/ui/palette-editor.js

@@ -133,7 +133,7 @@ RED.palette.editor = (function() {
         }).done(function(data,textStatus,xhr) {
             callback();
         }).fail(function(xhr,textStatus,err) {
-            callback(xhr);
+            callback(xhr,textStatus,err);
         });
     }
     function removeNodeModule(id,callback) {
@@ -1405,9 +1405,28 @@ RED.palette.editor = (function() {
                     RED.actions.invoke("core:show-event-log");
                 });
                 RED.eventLog.startEvent(RED._("palette.editor.confirm.button.install")+" : "+entry.id+" "+entry.version);
-                installNodeModule(entry.id,entry.version,entry.pkg_url,function(xhr) {
+                installNodeModule(entry.id,entry.version,entry.pkg_url,function(xhr, textStatus,err) {
                     spinner.remove();
-                     if (xhr) {
+                     if (err && xhr.status === 504) {
+                        var notification = RED.notify(RED._("palette.editor.errors.installTimeout"), {
+                            modal: true,
+                            fixed: true,
+                            buttons: [
+                                {
+                                    text: RED._("common.label.close"),
+                                    click: function() {
+                                        notification.close();
+                                    }
+                                },{
+                                    text: RED._("eventLog.view"),
+                                    click: function() {
+                                        notification.close();
+                                        RED.actions.invoke("core:show-event-log");
+                                    }
+                                }
+                            ]
+                        })
+                     } else if (xhr) {
                          if (xhr.responseJSON) {
                              var notification = RED.notify(RED._('palette.editor.errors.installFailed',{module: entry.id,message:xhr.responseJSON.message}),{
                                  type: 'error',

packages/node_modules/@node-red/runtime/lib/flows/util.js

@@ -68,7 +68,7 @@ function mapEnvVarProperties(obj,prop,flow,config) {
         if (obj[prop][0] === "$" && (EnvVarPropertyRE_old.test(v) || EnvVarPropertyRE.test(v)) ) {
             const envVar = v.substring(2,v.length-1);
             const r = redUtil.getSetting(config, envVar, flow);
-            if (r !== undefined && r !== '') {
+            if (r !== undefined) {
                 obj[prop] = r
             }
         }