Add missing gson dependency.
<groupId>org.jenkins-ci.plugins</groupId>
<artifactId>apache-httpcomponents-client-4-api</artifactId>
</dependency>
+ <dependency>
+ <groupId>com.google.code.gson</groupId>
+ <artifactId>gson</artifactId>
+ <version>2.8.8</version>
+ </dependency>
<!-- Optional Jenkins Plug-in Dependencies -->
<dependency>
