fix: allow null in CallGateChannel args

Dalamud/Plugin/Ipc/Exceptions/IpcValueNullError.cs

@@ -0,0 +1,21 @@
+using System;
+
+namespace Dalamud.Plugin.Ipc.Exceptions;
+
+/// <summary>
+/// This exception is thrown when a null value is passed to an IPC requiring a value type.
+/// </summary>
+public class IpcValueNullError : IpcError
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="IpcValueNullError"/> class.
+    /// </summary>
+    /// <param name="name">Name of the IPC.</param>
+    /// <param name="expectedType">The type expected.</param>
+    /// <param name="index">Index of the failing argument.</param>
+    public IpcValueNullError(string name, Type expectedType, int index)
+        : base($"IPC {name} expects a value type({expectedType.FullName}) at index {index}, null given.")
+    {
+        // ignored
+    }
+}

Dalamud/Plugin/Ipc/Internal/CallGateChannel.cs

@@ -105,7 +105,7 @@ namespace Dalamud.Plugin.Ipc.Internal
             var paramTypes = methodInfo.GetParameters()
                 .Select(pi => pi.ParameterType).ToArray();
 
-            if (args.Length != paramTypes.Length)
+            if (args?.Length != paramTypes.Length)
                 throw new IpcLengthMismatchError(this.Name, args.Length, paramTypes.Length);
 
             for (var i = 0; i < args.Length; i++)
@@ -113,6 +113,14 @@ namespace Dalamud.Plugin.Ipc.Internal
                 var arg = args[i];
                 var paramType = paramTypes[i];
 
+                if (arg == null)
+                {
+                    if (paramType.IsValueType)
+                        throw new IpcValueNullError(this.Name, paramType, i);
+
+                    continue;
+                }
+
                 var argType = arg.GetType();
                 if (argType != paramType)
                 {