client: promoted attributes widget: add placeholder for blank input fields

src/public/app/widgets/ribbon_widgets/promoted_attributes.js

@@ -155,6 +155,7 @@ export default class PromotedAttributesWidget extends NoteContextAwareWidget {
             .attr("data-attribute-type", valueAttr.type)
             .attr("data-attribute-name", valueAttr.name)
             .prop("value", valueAttr.value)
+            .prop("placeholder", t("promoted_attributes.unset-field-placeholder"))
             .addClass("form-control")
             .addClass("promoted-attribute-input")
             .on("change", (event) => this.promotedAttributeChanged(event));

src/public/translations/en/translation.json

@@ -824,6 +824,7 @@
   },
   "promoted_attributes": {
     "promoted_attributes": "Promoted Attributes",
+    "unset-field-placeholder": "not set",
     "url_placeholder": "http://website...",
     "open_external_link": "Open external link",
     "unknown_label_type": "Unknown label type '{{type}}'",

src/public/translations/ro/translation.json

@@ -944,7 +944,8 @@
     "remove_this_attribute": "Elimină acest atribut",
     "unknown_attribute_type": "Tip de atribut necunoscut „{{type}}”",
     "unknown_label_type": "Tip de etichetă necunoscut „{{type}}”",
-    "url_placeholder": "http://siteweb..."
+    "url_placeholder": "http://siteweb...",
+    "unset-field-placeholder": "nesetat"
   },
   "prompt": {
     "defaultTitle": "Aviz",