change function which loads magnetic field from get<IdealMagneticFieldRecord>().get(bfield) to get<IdealMagneticFieldRecord>().get(mfESInputTag, bfield) w/ mfESInputTag edm::ESInputTag which is constructed from the string parameter mfName. This parameter is set to "" as default value (in order to garuantee back-compatibility (i.e. standard magnetic field from DB) and it can be defined by config file as well