fix(frontend): remove the clear button from the dataset version picker

frontend/src/app/dashboard/component/user/user-dataset/user-dataset-explorer/dataset-detail.component.html

@@ -395,7 +395,6 @@ <h6 style="font-weight: lighter; font-size: 0.9em">Choose a Version:</h6>
                   <div class="select-and-button-container">
                     <nz-select
                       nzShowSearch
-                      nzAllowClear
                       nzPlaceHolder="Select a version"
                       (ngModelChange)="onVersionSelected($event)"
                       [(ngModel)]="selectedVersion">

frontend/src/app/dashboard/component/user/user-dataset/user-dataset-explorer/dataset-detail.component.spec.ts

@@ -704,6 +704,16 @@ describe("DatasetDetailComponent behavior", () => {
       expect(component.selectedVersionCreationTime).toMatch(/^\d{2}\/\d{2}\/\d{4} \d{2}:\d{2}:\d{2}$/);
     });
 
+    it("survives the version select being emptied", () => {
+      createComponent();
+      component.did = 5;
+
+      expect(() => component.onVersionSelected(undefined)).not.toThrow();
+
+      expect(component.selectedVersion).toBeUndefined();
+      expect(datasetServiceStub.retrieveDatasetVersionFileTree).not.toHaveBeenCalled();
+    });
+
     it("does not fetch a file tree for a version without a dvid", () => {
       createComponent();
       component.did = 5;
@@ -2422,6 +2432,11 @@ describe("DatasetDetailComponent rendered template", () => {
       expect(datasetService.retrieveDatasetVersionFileTree).toHaveBeenCalledWith(5, 13, true);
     });
 
+    it("offers no way to empty the selection", () => {
+      // Clearing it used to reach onVersionSelected as null and throw.
+      expect(fixture.nativeElement.querySelector("nz-select-clear, .ant-select-clear")).toBeNull();
+    });
+
     it("loads a picked version over the anonymous endpoint when nobody is signed in", () => {
       render({ isLogin: false });
 

frontend/src/app/dashboard/component/user/user-dataset/user-dataset-explorer/dataset-detail.component.ts

@@ -424,11 +424,11 @@ export class DatasetDetailComponent implements OnInit {
     this.isRightBarCollapsed = !this.isRightBarCollapsed;
   }
 
-  onVersionSelected(version: DatasetVersion): void {
+  onVersionSelected(version: DatasetVersion | undefined): void {
     this.selectedVersion = version;
-    if (this.did && this.selectedVersion.dvid)
+    if (this.did && version?.dvid)
       this.datasetService
-        .retrieveDatasetVersionFileTree(this.did, this.selectedVersion.dvid, this.isLogin)
+        .retrieveDatasetVersionFileTree(this.did, version.dvid, this.isLogin)
         .pipe(untilDestroyed(this))
         .subscribe(data => {
           this.fileTreeNodeList = data.fileNodes;