Fix rules

lib/models/rules/insert.dart

@@ -250,7 +250,8 @@ class ForceNewlineForInsertsAroundEmbedRule extends InsertRule {
 
     String text = data as String;
     DeltaIterator itr = DeltaIterator(document);
-    Operation prev = itr.skip(index), cur = itr.next();
+    final prev = itr.skip(index);
+    final cur = itr.next();
     bool cursorBeforeEmbed = cur.data is! String;
     bool cursorAfterEmbed = prev != null && prev.data is! String;
 

lib/models/rules/rule.dart

@@ -54,16 +54,20 @@ class Rules {
 
   Delta apply(RuleType ruleType, Document document, int index,
       {int len, Object data, Attribute attribute}) {
-    Delta delta = document.toDelta();
+    final delta = document.toDelta();
     for (var rule in _rules) {
       if (rule.type != ruleType) {
         continue;
       }
-      delta =
-          rule.apply(delta, index, len: len, data: data, attribute: attribute);
-      if (delta != null) {
+      try {
+        final result = rule.apply(delta, index,
+            len: len, data: data, attribute: attribute);
+        if (result != null) {
           print("Rule $rule applied");
-        return delta..trim();
+          return result..trim();
+        }
+      } catch (e) {
+        throw e;
       }
     }
     throw ('Apply rules failed');