fix(datepicker): added support for null value

Introduced support for null as default value:

- In the ngOnInit method of the datepicker-inner class the update should only emit when selectedDate is changed.
- Extra check in compare function
- activeDate() shouldn't return today when not set

fixes #16, closes #445

components/datepicker/datepicker-inner.ts

@@ -126,12 +126,12 @@ export class DatePickerInner implements OnInit {
 
     if (this.initDate) {
       this.activeDate = this.initDate;
+      this.selectedDate = new Date(this.activeDate.valueOf());
+      this.update.emit(this.activeDate);
     } else if (this.activeDate === undefined) {
       this.activeDate = new Date();
     }
-    this.selectedDate = new Date(this.activeDate.valueOf());
 
-    this.update.emit(this.activeDate);
     this.refreshView();
   }
 
@@ -150,6 +150,10 @@ export class DatePickerInner implements OnInit {
   }
 
   public compare(date1:Date, date2:Date):number {
+    if(date1=== undefined || date2 === undefined) {
+      return undefined;
+    }
+
     if (this.datepickerMode === 'day' && this.compareHandlerDay) {
       return this.compareHandlerDay(date1, date2);
     }

components/datepicker/datepicker.ts

@@ -1,7 +1,5 @@
 import {Component, Self, Input} from 'angular2/core';
-import {
-  CORE_DIRECTIVES, FORM_DIRECTIVES, ControlValueAccessor, NgModel
-} from 'angular2/common';
+import {CORE_DIRECTIVES, FORM_DIRECTIVES, ControlValueAccessor, NgModel} from 'angular2/common';
 import {DatePickerInner} from './datepicker-inner';
 import {DayPicker} from './daypicker';
 import {MonthPicker} from './monthpicker';
@@ -69,6 +67,7 @@ export class DatePicker implements ControlValueAccessor {
   public onTouched:any = Function.prototype;
 
   public cd:NgModel;
+  private _now:Date = new Date();
   private _activeDate:Date;
 
   @Input()
@@ -82,8 +81,6 @@ export class DatePicker implements ControlValueAccessor {
     cd.valueAccessor = this;
   }
 
-  private _now:Date = new Date();
-
   public set activeDate(value:Date) {
     this._activeDate = value;
   }