Make ternary expressions with an explicit null and another type return a nullable

[realbart]

Expressions like true ? 1 : null currently throw an exception:

error CS0173: Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and '<null>'

Therefore, the codebase I inherited contains many instances of:

Housenumber = int.TryParse(organization.HouseNumber, out var parsed) ? parsed : default(int?)

or

Housenumber = int.TryParse(organization.HouseNumber, out var parsed) ? (int?)parsed : null

or

Housenumber = int.TryParse(organization.HouseNumber, out var parsed) ? parsed : (int?)null

I'd like to be able to write:

Housenumber = int.TryParse(organization.HouseNumber, out var parsed) ? parsed : null

[yaakov-h]

Duplicate of #33 / #2460 / #2823