Warnings in Rec: "PyConf will not be able to infer this data dependency"

!2343 (merged) introduced new warnings in Rec: https://lhcb-nightlies.web.cern.ch/logs/build/nightly/lhcb-master/1321/x86_64-centos7-gcc9-opt/Rec/

# WARNING: String '' given as substitute for DataHandle; PyConf will not be able to infer this data dependency	
# WARNING: String '/Event/SOME/DUMMY/PATH' given as substitute for DataHandle; PyConf will not be able to infer this data dependency	
# WARNING: String 'Fake/Tracks' given as substitute for DataHandle; PyConf will not be able to infer this data dependency