[mono-cecil] Adding a method to a class

[harrison clarke]

so, i'm trying to add an instance method to a class. i tried this, but
it fails on write, because it can't find System.Object.

var asm = AssemblyDefinition.ReadAssembly(p);
        foreach (TypeDefinition def in asm.MainModule.Types) {
            Debug.Log(def.Name);
            if (def.Name == "Sample") {

                var t = new TypeReference("System", "Object", null,
null, false);
                var m = new MethodDefinition("Start",
MethodAttributes.Public, t);
                def.Methods.Add(m);
                Debug.Log("added start");
            }
        }
        asm.Write(p);

so, how would i get this to work?
also, how would i get the method to return void instead of an object?

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mono-cecil