isNullOrEmpty.swift

protocol StringType {
    var isEmpty: Bool { get }
}

extension String : StringType { }

extension Optional where Wrapped: StringType {
    var isNullOrEmpty: Bool {
        return self?.isEmpty ?? true
    }
}

extension Optional where Wrapped: CollectionType {
    var isNullOrEmpty: Bool {
        return self?.isEmpty ?? true
    }
}

// Strings:
let strs: [String?] = [nil, "", "Hello!"]
for s in strs {
    if s.isNullOrEmpty {
        print("null or empty string: \(s)")
    }
}

// Collections:
let colls: [[Int]?] = [nil, [], [1, 2, 3]]
for c in colls {
    if c.isNullOrEmpty {
        print("null or empty collection: \(c)")
    }
}

let filtered = colls.map({ $0?.lazy.filter({ $0 > 3 }) })
for c in filtered {
    if c.isNullOrEmpty {
        print("null or empty filtered collection: \(c)")
    }
}