GMS2 Error Code

obj_testfroggit:
___________________________________________
############################################################################################
FATAL ERROR in
action number 1
of  Step Event0
for object obj_testflowey:

Variable obj_testflowey.ST_characters(100012, -2147483648) not set before reading it.
 at gml_Script_scr_DialogJump (line 1) - ST_display_index = array_height_2d(ST_characters) - 1;
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Script_scr_DialogJump (line 1)
called from - gml_Object_obj_testflowey_Step_0 (line 27) -        scr_DialogJump();



obj_testflowey:
___________________________________________
############################################################################################
FATAL ERROR in
action number 1
of  Step Event0
for object obj_testfroggit:

Variable obj_testfroggit.ST_characters(100012, -2147483648) not set before reading it.
 at gml_Script_scr_DialogJump (line 1) - ST_display_index = array_height_2d(ST_characters) - 1;
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Script_scr_DialogJump (line 1)
called from - gml_Object_obj_testfroggit_Step_0 (line 27) -        scr_DialogJump();