checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">

<module name="Checker">

    <property name="severity" value="error"/>
    <property name="charset" value="UTF-8"/>
    <property name="fileExtensions" value="java, properties, xml, js, json"/>
    <module name="TreeWalker">
        <!--
        <module name="TodoComment">-->
            <!-- The (?i) below means Case Insensitive -->
        <!--<property name="format" value="(?i)FIXME"/>
-->
  <module name="RegexpSinglelineJava">
      <property name="format" value="org\.jetbrains\.annotations\.NotNull"/>
  </module>
  <module name="RegexpSinglelineJava">
      <property name="format" value="org\.jetbrains\.annotations\.Nullable"/>
  </module>
  <module name="RegexpSinglelineJava">
      <property name="format" value="org\.jetbrains\.annotations\.\*"/>
  </module>
</module>
</module>