Copy-From Troubles - Can I clear a field entry?

I’m trying to fix the Mutant Animals mod and have been encountering an error that I’m hoping has a simple solution I’ve overlooked. I think this particular bug came about when horse breeding was added, but the error is something many mods in my broken folder have.

Namely, when using “copy_from” I don’t know how to clear an entry from a field list, for this example, “reproduction” is the culprit. “baby_monster” and “baby_item” being the specific issue. I’ve seen “upgrades” cause similar issues. “into” and “into_group” specifically. The game hates when both of those options are present in a monster entry. I’ve only seen it happen when using “copy-from”. It doesn’t crash the load, but who knows how the game is resolving things, I’d rather specify one or the other.

So, does anyone know how to NULL out an entry within a field? I can overwrite it, but I’m entirely unclear on deleting it entirely. I could just nix the copy_from and build a complete monster to replace the problem one, but this seems like there should be a better solution or a guide I didn’t read or something. Plx help. I’ll share! Gonna do that anyway…

Mutant Animals creates a mutant horse which copies it’s stats from dda’s horse, which gives it vanilla horse breeding and most of the mutant versions work fine. But the mutant glue horse adds the ability to lay bone glue eggs. I think ending the line there is fine, I want to nix the “baby_monster” entry.

Vanilla Horse
    "id": "mon_horse",
    "type": "MONSTER",
    "name": { "str": "horse" },
    "description": "A hooved grazing mammal with a mane of hair, a sweeping tail, and powerful-looking muscles.  A stalwart companion to humans for longer than recorded history, with some effort you should be able to get this one to trust you enough to ride it.",
    "default_faction": "herbivore",
    "bodytype": "horse",
    "categories": [ "WILDLIFE" ],
    "species": [ "MAMMAL" ],
    "volume": "550000 ml",
    "weight": "550 kg",
    "hp": 90,
    "speed": 300,
    "attack_cost": 230,
    "material": [ "flesh" ],
    "symbol": "H",
    "color": "brown",
    "morale": 20,
    "melee_skill": 6,
    "melee_dice": 2,
    "melee_dice_sides": 12,
    "melee_cut": 0,
    "armor_elec": 1,
    "dodge": 2,
    "armor_bash": 2,
    "anger_triggers": [ "FRIEND_ATTACKED" ],
    "fear_triggers": [ "SOUND", "PLAYER_CLOSE" ],
    "placate_triggers": [ "PLAYER_WEAK" ],
    "harvest": "mammal_large_leather",
    "reproduction": { "baby_monster": "mon_horse_foal", "baby_count": 1, "baby_timer": 360 },
    "baby_flags": [ "SPRING", "SUMMER", "AUTUMN" ],
    "biosignature": { "biosig_item": "feces_manure", "biosig_timer": 2 },
    "special_attacks": [ [ "EAT_CROP", 60 ] ],
    "zombify_into": "mon_zombie_horse",
    "petfood": { "food": [ "CATTLEFOOD" ], "feed": "The %s seems to like you!  It lets you pat its head and seems friendly." },
Base Horse Mutant
    "abstract": "mon_horse_mutant",
    "type": "MONSTER",
    "copy-from": "mon_horse",
    "name": { "str": "mutant horse" },
    "categories": [ "NULL" ],
    "species": [ "MUTANT" ]
Problematic Glue Horse
    "id": "mon_horse_sick_glue",
    "type": "MONSTER",
    "copy-from": "mon_horse_mutant",
    "name": { "str": "glue horse" },
    "description": "A mutating horse that oozes a sticky substance from pulsing pores.  Driven mad by this affliction, the horse scratches itself against trees and buildings, leaving traces of disgusting glue everywhere it goes.",
    "reproduction": { "baby_egg": "bone_glue", "baby_count": 20, "baby_timer": 1 },
    "biosignature": { "biosig_item": "bone_glue", "biosig_timer": 1 },
    "color": "white"
Error Message Produced
DEBUG    : Both an egg and a live birth baby are defined for mon_horse_sick_glue

 FUNCTION : void MonsterGenerator::check_monster_definitions() const
 FILE     : /home/runner/work/Cataclysm-DDA/Cataclysm-DDA/android/app/jni/src/../../../../src/monstergenerator.cpp
 LINE     : 1445
 VERSION  : fdbe06d

TL/DR: Can one remove “baby_monster” entry from “reproduction” field to make way for horses that lay glue eggs without error messages? Should I? Will leaving the error in result in horses that lay glue eggs and occasionally have colts too? I’m too dug into sorting through the modpile to actually play the game to test…