Assume default constants always return valid 2da/ruleset values.

NWN.Anvil/src/main/API/Ruleset/NwBaseItem.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using NWN.Native.API;
@@ -371,15 +372,16 @@ public IEnumerable<DamageType> WeaponType
     /// Resolves a <see cref="NwBaseItem"/> from a <see cref="BaseItemType"/>.
     /// </summary>
     /// <param name="itemType">The item type to resolve.</param>
-    /// <returns>The associated <see cref="NwBaseItem"/> instance. Null if the base item type is invalid.</returns>
-    public static NwBaseItem? FromItemType(BaseItemType itemType)
+    /// <returns>The associated <see cref="NwBaseItem"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if itemType is not a value defined in baseitems.2da.</exception>
+    public static NwBaseItem FromItemType(BaseItemType itemType)
     {
-      return NwRuleset.BaseItems.ElementAtOrDefault((int)itemType);
+      return NwRuleset.BaseItems.ElementAt((int)itemType);
     }
 
-    public static implicit operator NwBaseItem?(BaseItemType itemType)
+    public static implicit operator NwBaseItem(BaseItemType itemType)
     {
-      return NwRuleset.BaseItems.ElementAtOrDefault((int)itemType);
+      return NwRuleset.BaseItems.ElementAt((int)itemType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/Ruleset/NwClass.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
@@ -336,15 +337,16 @@ public IReadOnlyList<ClassSpellGainList> SpellKnownTable
     /// Resolves a <see cref="NwClass"/> from a <see cref="Anvil.API.ClassType"/>.
     /// </summary>
     /// <param name="classType">The class type to resolve.</param>
-    /// <returns>The associated <see cref="NwClass"/> instance. Null if the class type is invalid.</returns>
-    public static NwClass? FromClassType(ClassType classType)
+    /// <returns>The associated <see cref="NwClass"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if classType is not a value defined in classes.2da.</exception>
+    public static NwClass FromClassType(ClassType classType)
     {
-      return NwRuleset.Classes.ElementAtOrDefault((int)classType);
+      return NwRuleset.Classes.ElementAt((int)classType);
     }
 
-    public static implicit operator NwClass?(ClassType classType)
+    public static implicit operator NwClass(ClassType classType)
     {
-      return NwRuleset.Classes.ElementAtOrDefault((int)classType);
+      return NwRuleset.Classes.ElementAt((int)classType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/Ruleset/NwDomain.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using NWN.Native.API;
@@ -70,15 +71,16 @@ internal NwDomain(byte domainId, CNWDomain domainInfo)
     /// Resolves a <see cref="NwDomain"/> from a <see cref="Domain"/>.
     /// </summary>
     /// <param name="domainType">The domain type to resolve.</param>
-    /// <returns>The associated <see cref="NwDomain"/> instance. Null if the domain type is invalid.</returns>
-    public static NwDomain? FromDomainType(Domain domainType)
+    /// <returns>The associated <see cref="NwDomain"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if domainType is not a value defined in domains.2da.</exception>
+    public static NwDomain FromDomainType(Domain domainType)
     {
-      return NwRuleset.Domains.ElementAtOrDefault((int)domainType);
+      return NwRuleset.Domains.ElementAt((int)domainType);
     }
 
-    public static implicit operator NwDomain?(Domain domainType)
+    public static implicit operator NwDomain(Domain domainType)
     {
-      return NwRuleset.Domains.ElementAtOrDefault((int)domainType);
+      return NwRuleset.Domains.ElementAt((int)domainType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/Ruleset/NwFaction.cs

@@ -105,20 +105,21 @@ internal NwFaction(CNWSFaction faction)
     /// Resolves a <see cref="NwFaction"/> from a <see cref="StandardFaction"/>.
     /// </summary>
     /// <param name="factionType">The faction type to resolve.</param>
-    /// <returns>The associated <see cref="NwFaction"/> instance. Null if the faction type is invalid.</returns>
-    public static NwFaction? FromStandardFaction(StandardFaction factionType)
+    /// <returns>The associated <see cref="NwFaction"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if factionType is not defined in the module faction list.</exception>
+    public static NwFaction FromStandardFaction(StandardFaction factionType)
     {
-      return FromFactionId((int)factionType);
+      return FromFactionId((int)factionType)!;
     }
 
     public static bool operator ==(NwFaction? left, NwFaction? right)
     {
       return Equals(left, right);
     }
 
-    public static implicit operator NwFaction?(StandardFaction faction)
+    public static implicit operator NwFaction(StandardFaction faction)
     {
-      return FromFactionId((int)faction);
+      return FromFactionId((int)faction)!;
     }
 
     public static bool operator !=(NwFaction left, NwFaction right)

NWN.Anvil/src/main/API/Ruleset/NwFeat.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
@@ -189,15 +190,16 @@ public IReadOnlyList<NwFeat> RequiredFeatsSome
     /// Resolves a <see cref="NwFeat"/> from a <see cref="Anvil.API.Feat"/>.
     /// </summary>
     /// <param name="featType">The feat type to resolve.</param>
-    /// <returns>The associated <see cref="NwFeat"/> instance. Null if the feat type is invalid.</returns>
-    public static NwFeat? FromFeatType(Feat featType)
+    /// <returns>The associated <see cref="NwFeat"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if featType is not a value defined in feats.2da.</exception>
+    public static NwFeat FromFeatType(Feat featType)
     {
-      return NwRuleset.Feats.ElementAtOrDefault((int)featType);
+      return NwRuleset.Feats.ElementAt((int)featType);
     }
 
-    public static implicit operator NwFeat?(Feat featType)
+    public static implicit operator NwFeat(Feat featType)
     {
-      return NwRuleset.Feats.ElementAtOrDefault((int)featType);
+      return NwRuleset.Feats.ElementAt((int)featType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/Ruleset/NwRace.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Linq;
 using NWN.Native.API;
 
@@ -120,15 +121,16 @@ internal NwRace(ushort raceId, CNWRace raceInfo)
     /// Resolves a <see cref="NwRace"/> from a <see cref="Anvil.API.RacialType"/>.
     /// </summary>
     /// <param name="racialType">The racial type to resolve.</param>
-    /// <returns>The associated <see cref="NwRace"/> instance. Null if the racial type is invalid.</returns>
-    public static NwRace? FromRacialType(RacialType racialType)
+    /// <returns>The associated <see cref="NwRace"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if racialType is not a value defined in racialtypes.2da.</exception>
+    public static NwRace FromRacialType(RacialType racialType)
     {
-      return NwRuleset.Races.ElementAtOrDefault((int)racialType);
+      return NwRuleset.Races.ElementAt((int)racialType);
     }
 
-    public static implicit operator NwRace?(RacialType racialType)
+    public static implicit operator NwRace(RacialType racialType)
     {
-      return NwRuleset.Races.ElementAtOrDefault((int)racialType);
+      return NwRuleset.Races.ElementAt((int)racialType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/Ruleset/NwSkill.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Linq;
 using NWN.Native.API;
 
@@ -80,15 +81,16 @@ internal NwSkill(byte skillId, CNWSkill skillInfo)
     /// Resolves a <see cref="NwSkill"/> from a <see cref="Anvil.API.Skill"/>.
     /// </summary>
     /// <param name="skillType">The skill type to resolve.</param>
-    /// <returns>The associated <see cref="NwSkill"/> instance. Null if the skill type is invalid.</returns>
-    public static NwSkill? FromSkillType(Skill skillType)
+    /// <returns>The associated <see cref="NwSkill"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if skillType is not a value defined in skills.2da.</exception>
+    public static NwSkill FromSkillType(Skill skillType)
     {
-      return NwRuleset.Skills.ElementAtOrDefault((int)skillType);
+      return NwRuleset.Skills.ElementAt((int)skillType);
     }
 
-    public static implicit operator NwSkill?(Skill skillType)
+    public static implicit operator NwSkill(Skill skillType)
     {
-      return NwRuleset.Skills.ElementAtOrDefault((int)skillType);
+      return NwRuleset.Skills.ElementAt((int)skillType);
     }
   }
 }

NWN.Anvil/src/main/API/Ruleset/NwSpell.cs

@@ -303,15 +303,16 @@ public SpellComponents SpellComponents
     /// Resolves a <see cref="NwSpell"/> from a <see cref="Anvil.API.Spell"/>.
     /// </summary>
     /// <param name="spellType">The spell type to resolve.</param>
-    /// <returns>The associated <see cref="NwSpell"/> instance. Null if the spell type is invalid.</returns>
-    public static NwSpell? FromSpellType(Spell spellType)
+    /// <returns>The associated <see cref="NwSpell"/> instance.</returns>
+    /// <exception cref="ArgumentOutOfRangeException">Thrown if spellType is not a value defined in spells.2da.</exception>
+    public static NwSpell FromSpellType(Spell spellType)
     {
-      return NwRuleset.Spells.ElementAtOrDefault((int)spellType);
+      return NwRuleset.Spells.ElementAt((int)spellType);
     }
 
-    public static implicit operator NwSpell?(Spell spellType)
+    public static implicit operator NwSpell(Spell spellType)
     {
-      return NwRuleset.Spells.ElementAtOrDefault((int)spellType);
+      return NwRuleset.Spells.ElementAt((int)spellType);
     }
 
     /// <summary>

NWN.Anvil/src/main/API/TwoDimArray/Tables/AppearanceTableEntry.cs

@@ -118,9 +118,9 @@ void ITwoDimArrayEntry.InterpretEntry(TwoDimArrayEntry entry)
       Targetable = entry.GetBool("TARGETABLE");
     }
 
-    public static implicit operator AppearanceTableEntry?(AppearanceType appearanceType)
+    public static implicit operator AppearanceTableEntry(AppearanceType appearanceType)
     {
-      return NwGameTables.AppearanceTable.ElementAtOrDefault((int)appearanceType);
+      return NwGameTables.AppearanceTable.ElementAt((int)appearanceType);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/EffectIconTableEntry.cs

@@ -31,9 +31,9 @@ public void InterpretEntry(TwoDimArrayEntry entry)
       StrRef = entry.GetStrRef("StrRef");
     }
 
-    public static implicit operator EffectIconTableEntry?(EffectIcon effectIcon)
+    public static implicit operator EffectIconTableEntry(EffectIcon effectIcon)
     {
-      return NwGameTables.EffectIconTable.ElementAtOrDefault((int)effectIcon);
+      return NwGameTables.EffectIconTable.ElementAt((int)effectIcon);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/ItemPropertyTableEntry.cs

@@ -66,9 +66,9 @@ void ITwoDimArrayEntry.InterpretEntry(TwoDimArrayEntry entry)
       Description = entry.GetStrRef("Description");
     }
 
-    public static implicit operator ItemPropertyTableEntry?(ItemPropertyType propertyType)
+    public static implicit operator ItemPropertyTableEntry(ItemPropertyType propertyType)
     {
-      return NwGameTables.ItemPropertyTable.ElementAtOrDefault((int)propertyType);
+      return NwGameTables.ItemPropertyTable.ElementAt((int)propertyType);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/PersistentVfxTableEntry.cs

@@ -107,9 +107,9 @@ public void InterpretEntry(TwoDimArrayEntry entry)
       return timeMs == null ? null : TimeSpan.FromMilliseconds(timeMs.Value);
     }
 
-    public static implicit operator PersistentVfxTableEntry?(PersistentVfxType vfxType)
+    public static implicit operator PersistentVfxTableEntry(PersistentVfxType vfxType)
     {
-      return NwGameTables.PersistentEffectTable.ElementAtOrDefault((int)vfxType);
+      return NwGameTables.PersistentEffectTable.ElementAt((int)vfxType);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/PolymorphTableEntry.cs

@@ -76,9 +76,9 @@ public void InterpretEntry(TwoDimArrayEntry entry)
       MergeA = entry.GetBool("MergeA");
     }
 
-    public static implicit operator PolymorphTableEntry?(PolymorphType polymorphType)
+    public static implicit operator PolymorphTableEntry(PolymorphType polymorphType)
     {
-      return NwGameTables.PolymorphTable.ElementAtOrDefault((int)polymorphType);
+      return NwGameTables.PolymorphTable.ElementAt((int)polymorphType);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/ProgrammedEffectTableEntry.cs

@@ -46,9 +46,9 @@ public void InterpretEntry(TwoDimArrayEntry entry)
       }
     }
 
-    public static implicit operator ProgrammedEffectTableEntry?(ProgFxType fxType)
+    public static implicit operator ProgrammedEffectTableEntry(ProgFxType fxType)
     {
-      return NwGameTables.ProgrammedEffectTable.ElementAtOrDefault((int)fxType);
+      return NwGameTables.ProgrammedEffectTable.ElementAt((int)fxType);
     }
   }
 }

NWN.Anvil/src/main/API/TwoDimArray/Tables/VisualEffectTableEntry.cs

@@ -91,9 +91,9 @@ void ITwoDimArrayEntry.InterpretEntry(TwoDimArrayEntry entry)
       OrientWithObject = entry.GetBool("OrientWithObject");
     }
 
-    public static implicit operator VisualEffectTableEntry?(VfxType vfxType)
+    public static implicit operator VisualEffectTableEntry(VfxType vfxType)
     {
-      return NwGameTables.VisualEffectTable.ElementAtOrDefault((int)vfxType);
+      return NwGameTables.VisualEffectTable.ElementAt((int)vfxType);
     }
   }
 }