mybatisplus set NULL

To set a column value to NULL in MyBatis Plus, you can use the `nullValue` property in the `@TableField` annotation or the `set` method when updating the entity.

1. Using `@TableField` annotation:

@TableField(nullValue = "NULL")
private String columnName;

2. Using the `set` method:

yourEntity.setColumnName(null);

By setting the column value to null, MyBatis Plus will generate the corresponding SQL statement to update the column with a NULL value in the database.