oh dear

mscorlib/System/Runtime/CompilerServices/AsyncStateMachineAttribute.cs

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+using System;
+using Cpp2IlInjected;
+
+namespace System.Runtime.CompilerServices
+{
+	/// <summary>Indicates whether a method is marked with either the Async or async modifier.</summary>
+	// Token: 0x0200053C RID: 1340
+	[Token(Token = "0x200053C")]
+	[AttributeUsage(AttributeTargets.Method)]
+	[Serializable]
+	public sealed class AsyncStateMachineAttribute : StateMachineAttribute
+	{
+		/// <summary>Initializes a new instance of the <see cref="T:System.Runtime.CompilerServices.AsyncStateMachineAttribute" /> class.</summary>
+		/// <param name="stateMachineType">The type object for the underlying state machine type that's used to implement a state machine method.</param>
+		// Token: 0x06002A2C RID: 10796 RVA: 0x00002050 File Offset: 0x00000250
+		[Token(Token = "0x6002A2C")]
+		[Address(RVA = "0x462000", Offset = "0x460E00", VA = "0x180462000")]
+		public AsyncStateMachineAttribute(Type stateMachineType)
+		{
+		}
+	}
+}