Prevent `null` contRules in CssRulesView

src/css_composer/view/CssRulesView.js

@@ -86,11 +86,13 @@ module.exports = require('backbone').View.extend({
       const container = fragment || this.el;
       let contRules;
 
-      // Try to find a specific container for the rule, if it
-      // containes a media query
+      // Try to find a specific container for the rule (if it
+      // containes a media query), otherwise get the default one
       try {
         contRules = container.querySelector(`#${blockId}`);
-      } catch (e) {
+      } catch (e) {}
+
+      if (!contRules) {
         contRules = container.querySelector(`#${defaultBlockId}`);
       }
 

test/specs/css_composer/view/CssRulesView.js

@@ -85,7 +85,11 @@ module.exports = {
             mediaText: '(max-width: 1000px)'
           },
           {
-            selectorsAdd: '#testid2',
+            selectorsAdd: '#testid3',
+            mediaText: '(min-width: 900px)'
+          },
+          {
+            selectorsAdd: '#testid4',
             mediaText: 'screen and (max-width: 900px) and (min-width: 600px)'
           }
         ];