Implemented the "isNil" and "isNotNil" properties in the Optional+Nil extension.

Sources/Core/Extensions/Optional+Nil.swift

@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the SwiftLibs open source project
+//
+// Copyright (c) 2023 Röck+Cöde VoF. and the SwiftLibs project authors
+// Licensed under the EUPL 1.2 or later.
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of SwiftLibs project authors
+//
+//===----------------------------------------------------------------------===//
+
+public extension Optional {
+    
+    // MARK: Properties
+    
+    /// A Boolean value indicating whether an optional has not been set.
+    var isNil: Bool { self == nil }
+    
+    /// A Boolean value indicating whether an optional has been set.
+    var isNotNil: Bool { !isNil }
+    
+}