Game crash when casting Spell gem? Overflow?

FATAL ERROR in
action number 1
of Step Event0
for object obj_battlecontroller:

Variable obj_battlecontroller.caster(100380, -2147483648) not set before reading it.
at gml_Script_bc_SpellDamage
############################################################################################

stack frame is
gml_Script_bc_SpellDamage (line 0)
gml_Script_bc_CreatureCast
gml_Script_bc_CreatureCastSpellGem
gml_Script_bc_EventDamage
gml_Script_bc_CreatureCast
gml_Script_bc_Turn
gml_Object_obj_battlecontroller_Step_0

Must have happened when my creature cast a spell. Don’t know what spell.
My damage is usually around 3-5B though.

Thanks! Will be fixed in the next patch.