fix(router): fix serializeQueryParams logic

corrects a bug that resulted in query params such as
`[queryParams]={a: 1, b:[]}` being serialized as 'a=1&'
instead of 'a=1'

resolves #42445

packages/router/src/url_tree.ts

@@ -502,7 +502,7 @@ function serializeQueryParams(params: {[key: string]: any}): string {
     return Array.isArray(value) ?
         value.map(v => `${encodeUriQuery(name)}=${encodeUriQuery(v)}`).join('&') :
         `${encodeUriQuery(name)}=${encodeUriQuery(value)}`;
-  });
+  }).filter(s => !!s);
 
   return strParams.length ? `?${strParams.join('&')}` : '';
 }

packages/router/test/create_url_tree.spec.ts

@@ -27,6 +27,16 @@ describe('createUrlTree', () => {
       expect(serializer.serialize(t2)).toEqual('/a/c/c2?m=v1&m=v2');
     });
 
+    it('should support parameter with empty arrays as values', () => {
+      const p1 = serializer.parse('/a/c');
+      const t1 = create(p1.root.children[PRIMARY_OUTLET], 1, p1, ['c2'], {m: []});
+      expect(serializer.serialize(t1)).toEqual('/a/c/c2');
+
+      const p2 = serializer.parse('/a/c');
+      const t2 = create(p2.root.children[PRIMARY_OUTLET], 1, p2, ['c2'], {m: [], n: 1});
+      expect(serializer.serialize(t2)).toEqual('/a/c/c2?n=1');
+    });
+
     it('should set query params', () => {
       const p = serializer.parse('/');
       const t = createRoot(p, [], {a: 'hey'});