Strict null pass on some base ui files (#4832)

* more strict null checks in base browser code

* revert changes to radiobutton

* fix some more minor things, enable strict null check in pipelines

* formatting

* fix compile errors

* make null undefined

* more null to undefined

src/sql/base/browser/ui/dropdownList/dropdownList.ts

@@ -98,7 +98,7 @@ export class DropdownList extends Dropdown {
 	 * Render the selected label of the dropdown
 	 */
 	public renderLabel(): void {
-		if (this._options.labelRenderer) {
+		if (this._options.labelRenderer && this.label) {
 			this._options.labelRenderer(this.label);
 		}
 	}