Failure when generating additional source code (Solved)

I followed this wiki page that gives guidelines for setting up local workspace. All other steps went fine but I encountered a failure when generating additional source code.
Here is the full log of the error when I ran ./gradlew assemble
Here is the error log when I ran ./gradlew assemble – stacktrace
Here is the error log when I ran ./gradlew assemble --info
Any one to help out because am currently blocked.
@tobiasdiez, @Siedlerchr, @koppor

Configuring JAVA_HOME in the .bashrc file and ensuring a stable internet connection overcomes the blocker as observed in this output. Thanks @Siedlerchr , @calixtus and @tobiasdiez for helping me out via https://gitter.im/JabRef/jabref :boom: