Find type of nullable properties via reflection

Nullable.GetUnderlyingType(fi.FieldType) will do the work for you check below code for do the thing you want

System.Reflection.FieldInfo[] fieldsInfos = typeof(NullWeAre).GetFields();

        foreach (System.Reflection.FieldInfo fi in fieldsInfos)
        {
            if (fi.FieldType.IsGenericType
                && fi.FieldType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
            {
                // We are dealing with a generic type that is nullable
                Console.WriteLine("Name: {0}, Type: {1}", fi.Name, Nullable.GetUnderlyingType(fi.FieldType));
            }

    }

possible solution:

    propertyType = propertyInfo[propertyInfoIndex].PropertyType;
    if (propertyType.IsGenericType &&
        propertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
    {
      propertyType = propertyType.GetGenericArguments()[0];
    }