Merge pull request #642 from JessonChan/develop

ignore nil time

@@ -144,8 +144,12 @@ func (d *dbBase) collectFieldValue(mi *modelInfo, fi *fieldInfo, ind reflect.Val
 				value = field.Interface()
 				value = field.Interface()
 				if t, ok := value.(time.Time); ok {
 				if t, ok := value.(time.Time); ok {
 					d.ins.TimeToDB(&t, tz)
 					d.ins.TimeToDB(&t, tz)
+					if t.IsZero() {
+						value = nil
+					} else {
 						value = t
 						value = t
 					}
 					}
+				}
 			default:
 			default:
 				switch {
 				switch {
 				case fi.fieldType&IsPostiveIntegerField > 0:
 				case fi.fieldType&IsPostiveIntegerField > 0: