Fix #207

Harmony/Internal/CodeTranspiler.cs

@@ -191,11 +191,16 @@ internal static IEnumerable ConvertToOurInstructions(IEnumerable instructions, T
 			}
 		}
 
+		static bool IsCodeInstructionsParameter(Type type)
+		{
+			return type.IsGenericType && type.GetGenericTypeDefinition().Name.StartsWith("IEnumerable", StringComparison.Ordinal);
+		}
+
 		internal static IEnumerable ConvertToGeneralInstructions(MethodInfo transpiler, IEnumerable enumerable, out Dictionary<object, Dictionary<string, object>> unassignedValues)
 		{
 			var type = transpiler.GetParameters()
 				  .Select(p => p.ParameterType)
-				  .FirstOrDefault(t => t.IsGenericType && t.GetGenericTypeDefinition().Name.StartsWith("IEnumerable", StringComparison.Ordinal));
+				  .FirstOrDefault(t => IsCodeInstructionsParameter(t));
 			return ConvertInstructionsAndUnassignedValues(type, enumerable, out unassignedValues);
 		}
 
@@ -208,7 +213,7 @@ internal static List<object> GetTranspilerCallParameters(ILGenerator generator,
 					parameter.Add(generator);
 				else if (type.IsAssignableFrom(typeof(MethodBase)))
 					parameter.Add(method);
-				else
+				else if (IsCodeInstructionsParameter(type))
 					parameter.Add(instructions);
 			});
 			return parameter;

Harmony/Internal/MethodCopier.cs

@@ -67,13 +67,18 @@ internal MethodBodyReader(MethodBase method, ILGenerator generator)
 
 			var body = method.GetMethodBody();
 			if (body == null)
-				throw new ArgumentException($"Method {method.FullDescription()} has no body");
-
-			var bytes = body.GetILAsByteArray();
-			if (bytes == null)
-				throw new ArgumentException($"Can not get IL bytes of method {method.FullDescription()}");
-			ilBytes = new ByteBuffer(bytes);
-			ilInstructions = new List<ILInstruction>((bytes.Length + 1) / 2);
+			{
+				ilBytes = new ByteBuffer(new byte[0]);
+				ilInstructions = new List<ILInstruction>();
+			}
+			else
+			{
+				var bytes = body.GetILAsByteArray();
+				if (bytes == null)
+					throw new ArgumentException("Can not get IL bytes of method " + method.FullDescription());
+				ilBytes = new ByteBuffer(bytes);
+				ilInstructions = new List<ILInstruction>((bytes.Length + 1) / 2);
+			}
 
 			var type = method.DeclaringType;
 
@@ -93,8 +98,8 @@ internal MethodBodyReader(MethodBase method, ILGenerator generator)
 				this_parameter = new ThisParameter(method);
 			parameters = method.GetParameters();
 
-			localVariables = body.LocalVariables?.ToList() ?? new List<LocalVariableInfo>();
-			exceptions = body.ExceptionHandlingClauses;
+			localVariables = body?.LocalVariables?.ToList() ?? new List<LocalVariableInfo>();
+			exceptions = body?.ExceptionHandlingClauses ?? new List<ExceptionHandlingClause>();
 		}
 
 		internal void ReadInstructions()

Harmony/Internal/MethodPatcher.cs

@@ -480,6 +480,9 @@ static bool AddPrefixes(ILGenerator il, MethodBase original, List<MethodInfo> pr
 			var canHaveJump = false;
 			prefixes.ForEach(fix =>
 			{
+				if (original.GetMethodBody() == null)
+					throw new Exception("Methods without body cannot have prefixes. Use a transpiler instead.");
+
 				EmitCallParameter(il, original, fix, variables, false);
 				Emitter.Emit(il, OpCodes.Call, fix);
 
@@ -500,6 +503,9 @@ static void AddPostfixes(ILGenerator il, MethodBase original, List<MethodInfo> p
 				.Where(fix => passthroughPatches == (fix.ReturnType != typeof(void)))
 				.Do(fix =>
 				{
+					if (original.GetMethodBody() == null)
+						throw new Exception("Methods without body cannot have postfixes. Use a transpiler instead.");
+
 					EmitCallParameter(il, original, fix, variables, true);
 					Emitter.Emit(il, OpCodes.Call, fix);
 
@@ -524,6 +530,9 @@ static bool AddFinalizers(ILGenerator il, MethodBase original, List<MethodInfo>
 			finalizers
 				.Do(fix =>
 				{
+					if (original.GetMethodBody() == null)
+						throw new Exception("Methods without body cannot have finalizers. Use a transpiler instead.");
+
 					if (catchExceptions)
 						Emitter.MarkBlockBefore(il, new ExceptionBlock(ExceptionBlockType.BeginExceptionBlock), out var label);