@ajeet1 This error seems to be due to the syntax error in the call for the clientlibs in your custom category created.
The correct syntax to call the clientlibs is
<sly data-sly-use.clientlib="/libs/granite/sightly/templates/clientlib.html"
data-sly-call="${clientlib.all @ categories='clientlib1,clientlib2'}"/>
This error appear in the build because of the "failOnWarnings" set as true in the plugin "htl-maven-plugin"
<plugin>
<groupId>org.apache.sling</groupId>
<artifactId>htl-maven-plugin</artifactId>
<version>2.0.2-1.4.0</version>
<configuration>
<failOnWarnings>true</failOnWarnings>
</configuration>
</plugin>
Thanks