BUILD FAILED: Cannot find an environment variable

BUILD FAILED: Cannot find an environment variable

I'm trying to build the TINOS/RINA project from
https://github.com/PouzinSociety/tinos/tree/development on Raspbian
(Raspberry Pi Debian).
Its instructions are to issue ant jar in the build directory, but when I
do so I get:
BUILD FAILED
/opt/tinos/projects/rina/build-rina/build.xml:34: Cannot find
/opt/tinos/projects/rina/build-rina/${env.TINOS_HOME}/projects/spring-build/tinos/package-top-level.xml
imported from /opt/tinos/projects/rina/build-rina/build.xml
So obviously there's an environment variable I'm missing somewhere, but is
it a Linux environment variable, or some sort of Java or Apache/ANT
variable? Where do I set it?
I tried set TINOS_HOME=/opt/tinos/ from command line, but that didn't
change anything.