Fix AutoExitBlockRule

lib/models/documents/attribute.dart

@@ -43,6 +43,27 @@ class Attribute<T> {
 
   static final BlockQuoteAttribute blockQuote = BlockQuoteAttribute();
 
+  static final Set<String> inlineKeys = {
+    Attribute.bold.key,
+    Attribute.italic.key,
+    Attribute.underline.key,
+    Attribute.strikeThrough.key,
+    Attribute.link.key
+  };
+
+  static final Set<String> blockKeys = {
+    Attribute.header.key,
+    Attribute.list.key,
+    Attribute.codeBlock.key,
+    Attribute.blockQuote.key,
+  };
+
+  static final Set<String> blockKeysExceptHeader = {
+    Attribute.list.key,
+    Attribute.codeBlock.key,
+    Attribute.blockQuote.key,
+  };
+
   static Attribute<int> get h1 => HeaderAttribute(level: 1);
 
   static Attribute<int> get h2 => HeaderAttribute(level: 2);

lib/models/rules/insert.dart

@@ -155,8 +155,12 @@ class AutoExitBlockRule extends InsertRule {
       return null;
     }
 
-    // retain(1) should be '\n', set it with no attribute (default to null)
-    return Delta()..retain(index)..retain(1);
+    final attributes = cur.attributes ?? <String, dynamic>{};
+    String k = attributes.keys
+        .firstWhere((k) => Attribute.blockKeysExceptHeader.contains(k));
+    attributes[k] = null;
+    // retain(1) should be '\n', set it with no attribute
+    return Delta()..retain(index)..retain(1, attributes);
   }
 }