validate ctor arguments (fixes #35112)

src/vs/workbench/api/node/extHostTypes.ts

@@ -1452,6 +1452,16 @@ export class RelativePattern implements IRelativePattern {
 	pattern: string;
 
 	constructor(base: vscode.WorkspaceFolder | string, pattern: string) {
+		if (typeof base !== 'string') {
+			if (!base || !URI.isUri(base.uri)) {
+				throw illegalArgument('base');
+			}
+		}
+
+		if (typeof pattern !== 'string') {
+			throw illegalArgument('pattern');
+		}
+
 		this.base = typeof base === 'string' ? base : base.uri.fsPath;
 		this.pattern = pattern;
 	}