升级mybatis版本.

https://github.com/baomidou/mybatis-plus/issues/2972

build.gradle

@@ -20,7 +20,7 @@ ext {
     ]
 
     libraries = [
-        mybatisVersion = '3.5.5',
+        mybatisVersion = '3.5.6',
         mybatisSpringVersion = '2.0.5',
         mybatisSpringBootStarterVersion = '2.1.3',
         springVersion = '5.2.8.RELEASE',