C# System.MissingMethodException

Question

I implemented a few Excel.Range extension methods which have been working fine for a while.

The following one still works (I specified Range with using Excel = Microsoft.Office.Interop.Excel; because Range also exists in System namespace):

public static T Get<T>(this Excel.Range range)
{
    var value = range.Value;

    if (range.Value is null)
    {
        return default;
    }

    try
    {
        return (T)value;
    }
    catch (Exception ex)
    {
        throw new Exception($"Unable to convert {range.Value.GetType()} to {typeof(T)}!", ex);
    }
}

but this one causes issue during the execution (not the compilation):

public static T? GetNullable<T>(this Excel.Range range) where T : struct
{
    if (range is null)
    {
        return null;
    }

    var value = range.Value;

    if (value is null)
    {
        return null;
    }

    if (value.ToString() == string.Empty)
    {
        return null;
    }

    return (T)value;
}

I encounter the following error from XUnit tests which rg.GetNullable<int>():

Message:  System.MissingMethodException : Method not found: 'System.Nullable`1<!!0>

Interop.Library.Helpers.RangeExtensionMethods.GetNullable(Microsoft.Office.Interop.Excel.Range)'.

Stack Trace: 

RangeExtensionMethods.GetNullable_NullInt_ReturnsNull()

RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)

MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

Does anyone have an idea what causes the issue? I clean the code and rebuild several times which has worked fine for a while.

Answer 1

I've just tested with a basic console app from scratch. If I include the GetNullable<T>() method within the console project, it works fine, but if I move it to a separate class library (minimalist from scratch) it also fails.

Now, I wonder if the error did not happen yesterday while I was transferring data from Excel (to SQLServer). I have a couple of table where I had no issue with the first ones, but got some errors then which I did not understand.

I did the same (duplicate the extension method) inside the library which deals with data access (CRUD methods) and it seems that everything is being transferred just fine.

I'll have a look to the other discussion when I get more time.

PS: I checked that I remove <Nullable>enable</Nullable> from all project properties.