fix crash when running EGAM derivations in trains in mc20/run2 data

Fix bug seen recently in ART tests https://bigpanda.cern.ch/art/jobs/?package=DerivationFrameworkTRainsART*&branch=master/Athena/x86_64-centos7-gcc11-opt&nlastnightlies=3&view=packages such as https://bigpanda.cern.ch//media/filebrowser/5bf3f056-5e79-4e46-8a67-7000e7ad764c/group.art/tarball_PandaJob_5675411972_ANALY_LRZ_VP/log.Derivation