org.apache.ibatis.exceptions.PersistenceException: 
### Error building SqlSession.
### The error may exist in mappers/user.xml
### Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: org.apache.ibatis.builder.BuilderException: Error parsing Mapper XML. The XML location is 'mappers/user.xml'. Cause: org.apache.ibatis.builder.BuilderException: Error resolving class. Cause: org.apache.ibatis.type.TypeException: Could not resolve type alias ''.  Cause: java.lang.ClassNotFoundException: Cannot find class: 

This error occurs in the mybatis test for many reasons,
1: it may be the header information error of the mapping file. Correct:

2: there may also be an error in the label of the mapping file. Most of the errors reported in the mapping file are code errors. Just check the code
3: I made an error today because I wrote an extra tag, but the content in the tag was not written

4: The same type of error I encountered yesterday is because I wrote a comment in the where tag

<select>
	<where>
		Write comment here. This error has been encountered twice, as soon as a comment is written inside a tag, an error is reported
	</where>
</select>

These are the mistakes and solutions I met in learning mybatis.