My solution was to insert <packaging>pom</packaging>
between artifactId
and version
<groupId>com.onlinechat</groupId>
<artifactId>chat-online</artifactId>
<packaging>pom</packaging>
<version>1.0-SNAPSHOT</version>
<modules>
<module>server</module>
<module>client</module>
<module>network</module>
</modules>