make sure to remove label tag from DOM if label is updated to NULL

inst/www/shared/shiny.js

@@ -4326,15 +4326,23 @@ function _defineProperty(obj, key, value) { if (key in obj) { Object.definePrope
     receiveMessage: function receiveMessage(el, data) {
       if (data.hasOwnProperty('value')) this.setValue(el, data.value);
 
+      var labelTag = $(el).parent().find('label[for="' + $escape(el.id) + '"]');
+      var hasLabelTag = labelTag.length > 0;
+
+      // If data.label exists, then we may need to insert a label
+      // tag into the DOM. If it doesn't exist, then the label tag
+      // should be removed to be more consistent with the behavior
+      // of `textInput(label = NULL)`
       if (data.hasOwnProperty('label')) {
-        var label = $(el).parent().find('label[for="' + $escape(el.id) + '"]');
-        // If textInput(label=NULL), then no label tag is provided from the
-        // server, so create one if we need to.
-        if (label.length === 0) {
-          $('<label for="' + $escape(el.id) + '">' + data.label + '</label>').insertBefore(el);
+
+        if (hasLabelTag) {
+          labelTag.text(data.label);
         } else {
-          label.text(data.label);
+          $('<label for="' + $escape(el.id) + '">' + data.label + '</label>').insertBefore(el);
         }
+      } else {
+
+        if (hasLabelTag) labelTag.remove();
       }
 
       if (data.hasOwnProperty('placeholder')) el.placeholder = data.placeholder;