Add tests for undefined query params

Fixes #169

modules/utils/__tests__/createSearch-test.js

@@ -5,6 +5,11 @@ describe('createSearch', () => {
     expect(createSearch({ a: 'a', b: '' })).toEqual('?a=a&b');
   });
 
+  it('omits the trailing = for null/undefined values', () => {
+    expect(createSearch({ a: 'a', b: null })).toEqual('?a=a&b');
+    expect(createSearch({ a: 'a', b: undefined })).toEqual('?a=a&b');
+  });
+
   it('sorts keys', () => {
     expect(createSearch({ b: 'b', a: 'a', c: 'c' })).toEqual('?a=a&b=b&c=c');
   });