diff --git a/README.md b/README.md
index 3af2d01b5..984c562ee 100644
--- a/README.md
+++ b/README.md
@@ -455,7 +455,7 @@ public final class JacksonCodec implements Codec<Object> {
         return encoding;
     }
 
-    private static final class JacksonParameter implements Parameter {
+    private static final class JacksonParameter implements MySqlParameter {
 
         private final ByteBufAllocator allocator;
 
@@ -524,6 +524,14 @@ public final class JacksonCodec implements Codec<Object> {
         public short getType() {
             return DataTypes.VARCHAR;
         }
+
+        /**
+         * Optional, for statements/parameters logging.
+         */
+        @Override
+        public String toString() {
+            return value.toString();
+        }
     }
 }
 ```
diff --git a/src/main/java/io/asyncer/r2dbc/mysql/codec/NullMySqlParameter.java b/src/main/java/io/asyncer/r2dbc/mysql/codec/NullMySqlParameter.java
index efce1cba5..f33ddee65 100644
--- a/src/main/java/io/asyncer/r2dbc/mysql/codec/NullMySqlParameter.java
+++ b/src/main/java/io/asyncer/r2dbc/mysql/codec/NullMySqlParameter.java
@@ -65,7 +65,6 @@ public void dispose() {
 
     @Override
     public String toString() {
-        // Hide parameter detail even it is null.
         return "null";
     }