Implemented the "empty" static constant for the String+Constants extension in the Foundation library.

Libraries/Foundation/Kit/Sources/Extensions/String+Constants.swift

@@ -0,0 +1,18 @@
+//
+//  String+Constants.swift
+//  ReviewsFoundation
+//
+//  Created by Javier Cicchelli on 16/03/2024.
+//  Copyright © 2024 Röck+Cöde VoF. All rights reserved.
+//
+
+import Foundation
+
+public extension String {
+    
+    // MARK: Constants
+    
+    /// A representation of an empty string.
+    static let empty: String = ""
+    
+}

Libraries/Foundation/Test/Tests/Extensions/String+ConstantsTests.swift

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+//
+//  String+ConstantsTests.swift
+//  ReviewsFoundationTest
+//
+//  Created by Javier Cicchelli on 16/03/2024.
+//  Copyright © 2024 Röck+Cöde VoF. All rights reserved.
+//
+
+import ReviewsFoundation
+import XCTest
+
+final class String_ConstantsTests: XCTestCase {
+    
+    // MARK: Properties
+    private var sut: String!
+    
+    // MARK: Constants tests
+    func testEmpty() throws {
+        // GIVEN
+        sut = .empty
+
+        // WHEN
+        // THEN
+        XCTAssertTrue(sut.isEmpty)
+    }
+    
+}