Existing AssemblyBuilder adds void type for null return type when populating the signature, now this scenario causing NRE in the SignatureHelper, I could fix it in the signature only, but to avoid NRE's for other case setting the return type to void here.

The constructor parameter, Type returnType isn't marked as nullable. If a null value is sneaking through, we should fix that or mark the parameter as nullable.

Yes, allowing null might was not intentional, but making it throw for null now probably will be breaking change. We might also want to move the null handling from SignatureHelper to RuntimePropertyBuilder

Sure, that makes sense. I don't think we should throw either, but I do like to have the nullable indicators correct so we can check these things.

Done

Existing AssemblyBuilder adds void type for null return type when populating the signature,

I assume this behavior exists in previous versions as well?

Yes, RuntimePropertyBuilder constructor was allowing null, but not handling null which could cause NRE further if SetConstant called for the property, the null has been resolved only for GetPropertySigHelper. I see same behavior in .NET framework.

Now with this PR the null return type will be handled to void type in the RuntimePropertyBuilder constructor, same as in GetPropertySigHelper.