A Null Reference Exception occurs when a surgery patient arrives, and the Operations page in the patient's health tab disappears:

System.NullReferenceException: Object reference not set to an instance of an object
[Ref CF6126E7]
at <0x178338f93f0 + 0x00173> <unknown method>
at MultiDoctorSurgery.Patches.Patch_HealthCardUtility_CreateSurgeryBill.Prefix (Verse.Pawn medPawn, Verse.RecipeDef recipe, Verse.BodyPartRecord part, System.Collections.Generic.List`1[T] uniqueIngredients, System.Boolean sendMessages) [0x000dc] in <7a97c59743844e0b94272e275b558173>:0
at RimWorld.HealthCardUtility.CreateSurgeryBill (Verse.Pawn medPawn, Verse.RecipeDef recipe, Verse.BodyPartRecord part, System.Collections.Generic.List`1[T] uniqueIngredients, System.Boolean sendMessages) [0x00030] in <2a40c3593b334f29ac3cb3d32d652351>:0
- PREFIX com.multidoctor.surgery: Boolean MultiDoctorSurgery.Patches.Patch_HealthCardUtility_CreateSurgeryBill:Prefix(Pawn medPawn, RecipeDef recipe, BodyPartRecord part, List`1 uniqueIngredients, Boolean sendMessages)
at Hospital.Utilities.SurgeryUtility.AddRandomSurgeryBill (Verse.Pawn pawn, Hospital.PatientData patientData, Hospital.HospitalMapComponent hospital) [0x00834] in <8d4aece5b2e4443d8292071025d48aab>:0
at Hospital.Utilities.PatientUtility.DamagePawn (Verse.Pawn pawn, Hospital.PatientData patientData, Hospital.HospitalMapComponent hospital) [0x00032] in <8d4aece5b2e4443d8292071025d48aab>:0
at Hospital.IncidentWorker_PatientArrives.SpawnPatient (Verse.Map map, Verse.Pawn pawn) [0x000bf] in <8d4aece5b2e4443d8292071025d48aab>:0
at Hospital.IncidentWorker_PatientArrives.TryExecuteWorker (RimWorld.IncidentParms parms) [0x000f2] in <8d4aece5b2e4443d8292071025d48aab>:0
at Hospital.IncidentScheduler.MapComponentTick () [0x00076] in <8d4aece5b2e4443d8292071025d48aab>:0
at Verse.MapComponentUtility.MapComponentTick (Verse.Map map) [0x00013] in <2a40c3593b334f29ac3cb3d32d652351>:0
UnityEngine.StackTraceUtility:ExtractStackTrace ()
Verse.Log:Error (string)
Verse.MapComponentUtility:MapComponentTick (Verse.Map)
Verse.Map:MapPostTick ()
Verse.TickManager:DoSingleTick ()
Verse.TickManager:TickManagerUpdate ()
Verse.Game:UpdatePlay ()
Verse.Root_Play:Update ()

I've tested this with only these two mods enabled. Here's my mod list:

- brrainz.harmony
- Ludeon.RimWorld
- Ludeon.RimWorld.Royalty
- Ludeon.RimWorld.Ideology
- Ludeon.RimWorld.Biotech
- Ludeon.RimWorld.Anomaly
- MasterPNJ.MultiDoctor
- Adamas.Hospital

The error still occurs after I swapped the mod loading order.

I'll also notify the author of Multi-doctor surgery about this issue, but it would be great if the operation bill were not automatically assigned to the patient in the Hospital Mod.