fix(service): fix interpolation issue with non-string as input

Since AngularJS 1.5, the input values (i.e. of a filter) will used 'as is' which means numbers (as translation ids) will not be transformed to strings anymore. This generates unexpected errors.

Because this fix, the result is that explicit typed number values will be return (transformed as a string).

```
// before and < AJS 1.5
$filter('translate)(0) === 0
// after and < AJS 1.5
$filter('translate)(0) === '0'

// before and AJS 1.5+
$filter('translate)(0) exception
// after and AJS 1.5+
$filter('translate)(0) === '0'

```

Fixes #1511

src/service/default-interpolation.js

@@ -66,17 +66,29 @@ function $translateDefaultInterpolation ($interpolate, $translateSanitization) {
    * @methodOf pascalprecht.translate.$translateDefaultInterpolation
    *
    * @description
-   * Interpolates given string agains given interpolate params using angulars
+   * Interpolates given value agains given interpolate params using angulars
    * `$interpolate` service.
    *
+   * Since AngularJS 1.5, `value` must not be a string but can be anything input.
+   *
    * @returns {string} interpolated string.
    */
-  $translateInterpolator.interpolate = function (string, interpolationParams) {
+  $translateInterpolator.interpolate = function (value, interpolationParams) {
     interpolationParams = interpolationParams || {};
     interpolationParams = $translateSanitization.sanitize(interpolationParams, 'params');
 
-    var interpolatedText = $interpolate(string)(interpolationParams);
-    interpolatedText = $translateSanitization.sanitize(interpolatedText, 'text');
+    var interpolatedText;
+    if (angular.isNumber(value)) {
+      // numbers are safe
+      interpolatedText = '' + value;
+    } else if (angular.isString(value)) {
+      // strings must be interpolated (that's the job here)
+      interpolatedText = $interpolate(value)(interpolationParams);
+      interpolatedText = $translateSanitization.sanitize(interpolatedText, 'text');
+    } else {
+      // neither a number or a string, cant interpolate => empty string
+      interpolatedText = '';
+    }
 
     return interpolatedText;
   };

test/unit/filter/translate.spec.js

@@ -317,4 +317,64 @@ describe('pascalprecht.translate', function () {
       expect(element.html()).toBe('Hallo');
     });
   });
+
+  describe('filter handling a falsy value', function () {
+
+    beforeEach(module('pascalprecht.translate', function ($translateProvider) {
+      $translateProvider
+        .translations('en', {
+          'HELLO': 'Hello'
+        })
+        .translations('de', {
+          'HELLO': 'Hallo'
+        })
+        .preferredLanguage('en');
+    }));
+
+    var $translate, $rootScope, $compile;
+    beforeEach(inject(function (_$rootScope_, _$compile_, _$translate_) {
+      $rootScope = _$rootScope_;
+      $compile = _$compile_;
+      $translate = _$translate_;
+    }));
+
+    it('should work with "0"', function () {
+      var element = $compile('<div>{{0 | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('0');
+    });
+
+    it('should work with "false"', function () {
+      var element = $compile('<div>{{false | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('');
+    });
+
+    it('should work with "null"', function () {
+      var element = $compile('<div>{{null | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('');
+    });
+
+    it('should work with "0" (by scope)', function () {
+      $rootScope.x = 0;
+      var element = $compile('<div>{{x | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('0');
+    });
+
+    it('should work with "false" (by scope)', function () {
+      $rootScope.x = false;
+      var element = $compile('<div>{{x | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('');
+    });
+
+    it('should work with "null" (by scope)', function () {
+      $rootScope.x = null;
+      var element = $compile('<div>{{x | translate}}</div>')($rootScope);
+      $rootScope.$digest();
+      expect(element.html()).toBe('');
+    });
+  });
 });