fix(ng1.stateService): Coerce 'null' params value to empty object

Closes #2952

src/state/stateService.ts

@@ -460,19 +460,20 @@ export class StateService {
  *
  * @returns {string} compiled state url
  */
- href(stateOrName: StateOrName, params?: RawParams, options?: HrefOptions): string {
+ href(stateOrName: StateOrName, params: RawParams, options?: HrefOptions): string {
  let defaultHrefOpts = {
  lossy: true,
  inherit: true,
  absolute: false,
  relative: this.$current
  };
  options = defaults(options, defaultHrefOpts);
+ params = params || {};
 
  let state = this.router.stateRegistry.matcher.find(stateOrName, options.relative);
 
  if (!isDefined(state)) return null;
- if (options.inherit) params = <any> this.params.$inherit(params || {}, this.$current, state);
+ if (options.inherit) params = <any> this.params.$inherit(params, this.$current, state);
 
  let nav = (state && options.lossy) ? state.navigable : state;