MC-3966: Block type errors when no block is selected and grid is empty

- Added type checks for empty values

Author: nathanjosiah

app/code/Magento/PageBuilder/view/adminhtml/web/js/content-type/block/preview.js

@@ -64,7 +64,7 @@ define([
             var requestData = $.extend(true, {}, this.requestData);
 
             // The component hasn't be configured yet. Nothing to do.
-            if (!this.id() || !this.requestParameter || !this.dataUrlConfigPath) {
+            if (!this.id().length || !this.requestParameter || !this.dataUrlConfigPath) {
                 return;
             }
 

app/code/Magento/PageBuilder/view/adminhtml/web/js/form/element/block-chooser.js

@@ -88,7 +88,7 @@ export default class Preview extends BasePreview {
             this.placeholderText("");
         }
 
-        if (!data.block_id || data.template.length === 0) {
+        if (!data.block_id || (data.block_id && data.block_id.length === 0) || data.template.length === 0) {
             this.showBlockPreview(false);
             this.placeholderText(this.messages.NOT_SELECTED);
             return;