🐛 Fixed error in translate helper when invalid parameters are passed (#20663)

ref https://linear.app/tryghost/issue/SLO-182
ref https://github.com/TryGhost/Ghost/issues/15500

- when the {{ t }} helper is used with no parameter or an empty string,
it now returns an empty string
- when the {{ t }} helper is used without options, it now does not throw
an error

ghost/core/core/frontend/helpers/t.js

@@ -11,18 +11,11 @@
 // {{tags prefix=(t " on ")}}
 
 const {themeI18n} = require('../services/handlebars');
-const errors = require('@tryghost/errors');
-const tpl = require('@tryghost/tpl');
 
-const messages = {
-    oopsErrorTemplateHasError: 'Oops, seems there is an error in the template.'
-};
-
-module.exports = function t(text, options) {
-    if (text === undefined && options === undefined) {
-        throw new errors.IncorrectUsageError({
-            message: tpl(messages.oopsErrorTemplateHasError)
-        });
+module.exports = function t(text, options = {}) {
+    if (!text || text.length === 0) {
+        // no-op: translation key is missing, return an empty string
+        return '';
     }
 
     const bindings = {};

ghost/core/core/frontend/services/theme-engine/i18n/I18n.js

@@ -165,7 +165,7 @@ class I18n {
         let matchingString;
 
         // no path? no string
-        if (msgPath.length === 0 || !isString(msgPath)) {
+        if (!msgPath || msgPath.length === 0 || !isString(msgPath)) {
             this._handleEmptyKeyError();
             return '';
         }

ghost/core/test/unit/frontend/helpers/t.test.js

@@ -53,4 +53,28 @@ describe('{{t}} helper', function () {
 
         rendered.should.eql('Top left Button');
     });
+
+    it('returns an empty string if translation key is an empty string', function () {
+        let rendered = t.call({}, '', {
+            hash: {}
+        });
+
+        rendered.should.eql('');
+    });
+
+    it('returns an empty string if translation key is missing', function () {
+        let rendered = t.call({}, undefined, {
+            hash: {}
+        });
+
+        rendered.should.eql('');
+    });
+
+    it('returns a translated string even if no options are passed', function () {
+        themeI18n.init({activeTheme: 'locale-theme', locale: 'en'});
+
+        let rendered = t.call({}, 'Top left Button');
+
+        rendered.should.eql('Left Button on Top');
+    });
 });