This gist is a slightly modified version from the plunker of Emil van Galen. It basically forces angular to set a ng-model value to null instead of an empty string (when this directive is applied and the model value is empty). a blog post about the issue and some additional solutions can be found here: (http://blog.jdriven.com/2013/09/how-angula…

fixParsingInconsistencies.js

'use strict';

angular.module('ModuleName')
  .directive('fixParsingInconsistencies', function () {
    return {
      require: '?ngModel',
      priority: (angular.version.full.indexOf('1.2.') === 0 &&
                 angular.version.full !== '1.2.0rc1' &&
                 angular.version.full !== '1.2.0-rc.2') ? 1 : 0,
      restrict: 'A',
      link: function (scope, element, attrs, ngModelController) {
        ngModelController.$parsers.push(function (value) {
          if ((ngModelController.$invalid && angular.isUndefined(value)) || value === '') {
            return null;
          } else {
            return value;
          }
        });
      }
    };
  });