fix #39865

src/vs/workbench/browser/parts/editor/editorActions.ts

@@ -323,13 +323,15 @@ export abstract class BaseFocusSideGroupAction extends Action {
 		else if (referenceEditor) {
 			const history = this.historyService.getHistory();
 			for (let input of history) {
-				if (input instanceof EditorInput && input.supportsSplitEditor()) {
+				if (input instanceof EditorInput) {
+					if (input.supportsSplitEditor()) {
 						return this.editorService.openEditor(input, { pinned: true }, this.getTargetEditorSide());
 					}
-
+				} else {
 					return this.editorService.openEditor({ resource: (input as IResourceInput).resource, options: { pinned: true } }, this.getTargetEditorSide());
 				}
 			}
+		}
 
 		return TPromise.as(true);
 	}