[Editor] Avoid an exception when copying an existing editor

src/display/editor/editor.js

@@ -493,8 +493,9 @@ class AnnotationEditor {
    * new annotation to add to the pdf document.
    *
    * To implement in subclasses.
+   * @param {boolean} isForCopying
    */
-  serialize() {
+  serialize(_isForCopying = false) {
     unreachable("An editor must be serializable");
   }
 

src/display/editor/freetext.js

@@ -567,7 +567,7 @@ class FreeTextEditor extends AnnotationEditor {
   }
 
   /** @inheritdoc */
-  serialize() {
+  serialize(isForCopying = false) {
     if (this.isEmpty()) {
       return null;
     }
@@ -596,13 +596,20 @@ class FreeTextEditor extends AnnotationEditor {
       pageIndex: this.pageIndex,
       rect,
       rotation: this.rotation,
-      id: this.annotationElementId,
     };
 
+    if (isForCopying) {
+      // Don't add the id when copying because the pasted editor mustn't be
+      // linked to an existing annotation.
+      return serialized;
+    }
+
     if (this.annotationElementId && !this.#hasElementChanged(serialized)) {
       return null;
     }
 
+    serialized.id = this.annotationElementId;
+
     return serialized;
   }
 

src/display/editor/tools.js

@@ -555,11 +555,8 @@ class AnnotationEditorUIManager {
 
     const editors = [];
     for (const editor of this.#selectedEditors) {
-      if (!editor.isEmpty()) {
-        const serialized = editor.serialize();
-        // Remove the id from the serialized data because it mustn't be linked
-        // to an existing annotation.
-        delete serialized.id;
+      const serialized = editor.serialize(/* isForCopying = */ true);
+      if (serialized) {
         editors.push(serialized);
       }
     }