Cherry pick changes from #3492298.

build/js/entity_browser.modal_selection.js

@@ -19,9 +19,12 @@
       .trigger('entities-selected', [drupalSettings.entity_browser.modal.uuid, drupalSettings.entity_browser.modal.entities])
       .unbind('entities-selected').show();
 
-    // This closes the mercury-dialog.
-    Array.from(parent.document.querySelectorAll('.entity-browser-modal-iframe')).forEach((element) => { element.closest('mercury-dialog').close(); });
+    // If there is a mercury-dialog element, close it. This code fires even on pages that do not have Mercury Editor so the element may not exist.
+    Array.from(parent.document.querySelectorAll('.entity-browser-modal-iframe')).forEach((element) => {
+      element.closest('mercury-dialog')?.close();
+    });
 
+    // TODO: Find a solution to attach Mercury libraries only to pages that have Mercury Editor.
   })(drupalSettings);
 
 })();

build/js/entity_browser.modal_selection.min.js

-!function(){"use strict";!function(e){parent.jQuery(parent.document).find(":input[data-uuid*="+e.entity_browser.modal.uuid+"]").trigger("entities-selected",[e.entity_browser.modal.uuid,e.entity_browser.modal.entities]).unbind("entities-selected").show(),Array.from(parent.document.querySelectorAll(".entity-browser-modal-iframe")).forEach((e=>{e.closest("mercury-dialog").close()}))}(drupalSettings)}();
+!function(){"use strict";!function(e){parent.jQuery(parent.document).find(":input[data-uuid*="+e.entity_browser.modal.uuid+"]").trigger("entities-selected",[e.entity_browser.modal.uuid,e.entity_browser.modal.entities]).unbind("entities-selected").show(),Array.from(parent.document.querySelectorAll(".entity-browser-modal-iframe")).forEach((e=>{e.closest("mercury-dialog")?.close()}))}(drupalSettings)}();

source/js/entity_browser.modal_selection.js

+'use strict';
+
 /**
  * @file entity_browser.modal_selection.js
  *
@@ -5,7 +7,6 @@
  */
 
 (function (drupalSettings) {
-  'use strict';
 
   // For some reason, Entity Browser does not close the modal with Ajax commands.
   // We follow their lead in how they close the modal.
@@ -17,7 +18,11 @@
     .trigger('entities-selected', [drupalSettings.entity_browser.modal.uuid, drupalSettings.entity_browser.modal.entities])
     .unbind('entities-selected').show();
 
-  // This closes the mercury-dialog.
-  Array.from(parent.document.querySelectorAll('.entity-browser-modal-iframe')).forEach((element) => { element.closest('mercury-dialog').close(); });
+  // If there is a mercury-dialog element, close it. This code fires even on pages that do not have Mercury Editor so the element may not exist.
+  Array.from(parent.document.querySelectorAll('.entity-browser-modal-iframe')).forEach((element) => {
+    element.closest('mercury-dialog')?.close();
+  });
 
+  // TODO: Find a solution to attach Mercury libraries only to pages that have Mercury Editor.
 })(drupalSettings);
+