Language: Support null in arrays

[tomsontom]

Currently the language does not allow one to express that an entry in an array can be null.

Currently we can express

• Array is optional: name?: string[]
• Array is nullable: name: string[]?
• Array is optional and nullable: name?: string[]?

Possible construct:

• string?[] - might look strange if string?[]? - not sure we can express it in the grammer
• string() - looks like a function call
• nullable<string>[] - eats another keyword and from an editing point of view it feels wrong
• string | null[] - feels wrong because then we'd express null always using | null instead of ?

another option might be that we change the syntax to create defined an array:

• array<string> - array of strings
• array<string>? - array of strings or null
• array<string?> - array of strings/null
• array<string?>? - arrary of string/null or null

this has the disavantage that for the default case the string[] this looks strange and unnatural and we'd add another keyword to the language