GMS2 Error Code ItemMenu

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FATAL ERROR in
action number 1
of Draw Event
for object obj_inventory:

Variable obj_inventory.ST_display_index(100015, -2147483648) not set before reading it.
 at gml_Script_scr_Dialog (line 258) - if ST_display_index < array_height_2d(ST_characters) - 1
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stack frame is
gml_Script_scr_Dialog (line 258)
called from - gml_Object_obj_inventory_Draw_64 (line 9) -               DoneSpeaking = scr_Dialog(Text_X, Text_Y, Item_String_Display_USE, StringSep, MaxStringWidth, c_white, fnt_underfont_1, 1, voice_ut, 1, 0, obj_inventory, ev_user0, ev_user1);