fix(interpolate): do not try to optimize by removing empty strings

To make sure a string is always returned

Author: vicb

lib/core/interpolate.dart

@@ -27,10 +27,11 @@ class Interpolate implements Function {
 
   String call(String template, [bool mustHaveExpression = false,
       String startSymbol = '{{', String endSymbol = '}}']) {
+    if (template == null || template.isEmpty) return "";
 
-    int startLen = startSymbol.length;
-    int endLen = endSymbol.length;
-    int length = template.length;
+    final startLen = startSymbol.length;
+    final endLen = endSymbol.length;
+    final length = template.length;
 
     int startIdx;
     int endIdx;
@@ -45,9 +46,7 @@ class Interpolate implements Function {
       startIdx = template.indexOf(startSymbol, index);
       endIdx = template.indexOf(endSymbol, startIdx + startLen);
       if (startIdx != -1 && endIdx != -1) {
-        if (index < startIdx) {
-          expParts.add('"${template.substring(index, startIdx)}"');
-        }
+        expParts.add('"${template.substring(index, startIdx)}"');
         expParts.add('(${template.substring(startIdx + startLen, endIdx)})');
         index = endIdx + endLen;
         hasInterpolation = true;

lib/core_dom/ng_mustache.dart

@@ -16,7 +16,7 @@ class NgTextMustacheDirective {
   }
 
   void _updateMarkup(text, previousText) {
-    if (text != previousText) _element.text = text.toString();
+    if (text != previousText) _element.text = text;
   }
 }
 
@@ -48,7 +48,7 @@ class NgAttrMustacheDirective {
   }
 
   void _updateMarkup(text, previousText) {
-    if (previousText != text) _attrs[_attrName] = text.toString();
+    if (previousText != text) _attrs[_attrName] = text;
   }
 }
 

lib/directive/ng_pluralize.dart

@@ -174,6 +174,6 @@ class NgPluralizeDirective {
   }
 
   void _updateMarkup(text, previousText) {
-    if (text != previousText) element.text = text.toString();
+    if (text != previousText) element.text = text;
   }
 }

test/core/interpolate_spec.dart

@@ -18,10 +18,11 @@ main() {
       expect($interpolate('Hello {{name}}!')).toEqual('"Hello "+(name)+"!"');
       expect($interpolate('a{{b}}C')).toEqual('"a"+(b)+"C"');
       expect($interpolate('a{{b}}')).toEqual('"a"+(b)');
-      expect($interpolate('{{a}}b')).toEqual('(a)+"b"');
-      expect($interpolate('{{b}}')).toEqual('(b)');
-      expect($interpolate('{{b}}+{{c}}')).toEqual('(b)+"+"+(c)');
-      expect($interpolate('{{b}}x{{c}}')).toEqual('(b)+"x"+(c)');
+      expect($interpolate('{{a}}b')).toEqual('""+(a)+"b"');
+      expect($interpolate('{{a}}{{b}}')).toEqual('""+(a)+""+(b)');
+      expect($interpolate('{{b}}')).toEqual('""+(b)');
+      expect($interpolate('{{b}}+{{c}}')).toEqual('""+(b)+"+"+(c)');
+      expect($interpolate('{{b}}x{{c}}')).toEqual('""+(b)+"x"+(c)');
     });
 
     it('should Parse Multiline', (Interpolate $interpolate) {