title: What does the error message "com.mysql.cj.exceptions.WrongArgumentException: The database URL cannot be null." mean?
body: <p>I'm working on a Spring Boot project with MySQL Database. If I run my code, a <code>WrongArgumentException</code> saying that the <code>databaseURL cannot be null</code>. </p>
  
  <p>application.properties:</p>
  
  <pre><code>spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
  spring.datasource.jdbc-url=jdbc:mysql//localhost:3306/reserving?autoReconnect=true&amp;amp;useSSL=false
  spring.datasource.username=root
  spring.datasource.password=****
  
  ##Mapper Config##
  mybatis.type-aliases-package=com.springboot.reserving
  mybatis.mapper-locations=mapper/**/*.xml
  
  spring.devtools.livereload.enabled =true
  
  spring.freemarker.cache=false
  </code></pre>
  
  <p>Error message:</p>
  
  <pre><code>java.sql.SQLNonTransientConnectionException: Cannot load connection class
   because of underlying exception: 
  com.mysql.cj.exceptions.WrongArgumentException: The database URL cannot be null.
  </code></pre>