diff --git a/Sources/ValidationKit/Validators/Validator+Empty.swift b/Sources/ValidationKit/Validators/Validator+Empty.swift
index f87c436..5d18c54 100644
--- a/Sources/ValidationKit/Validators/Validator+Empty.swift
+++ b/Sources/ValidationKit/Validators/Validator+Empty.swift
@@ -7,14 +7,13 @@
 
 import Foundation
 
-public extension Validator {
+public extension Validator where Input == String?, Output == String {
   /// The value must be empty
   static var isEmpty: Validator<String?, String> {
     Validator<String?, String> { input in
-      let val = input?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines) ?? ""
-
-      if val.isEmpty {
-        return .valid(val)
+      let input = input?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines) ?? ""
+      if input.isEmpty {
+        return .valid(input)
       } else {
         return .invalid(.isEmpty)
       }
@@ -24,7 +23,34 @@ public extension Validator {
   /// The value must not be empty
   static var notEmpty: Validator<String?, String> {
     Validator<String?, String> { input in
-      if let input = input?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines), !input.isEmpty {
+      let input = input?.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines) ?? ""
+      if !input.isEmpty {
+        return .valid(input)
+      } else {
+        return .invalid(.notEmpty)
+      }
+    }
+  }
+}
+
+public extension Validator where Input == String, Output == String {
+  /// The value must be empty
+  static var isEmpty: Validator<String, String> {
+    Validator<String, String> { input in
+      let input = input.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
+      if input.isEmpty {
+        return .valid(input)
+      } else {
+        return .invalid(.isEmpty)
+      }
+    }
+  }
+
+  /// The value must not be empty
+  static var notEmpty: Validator<String, String> {
+    Validator<String, String> { input in
+      let input = input.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines)
+      if !input.isEmpty {
         return .valid(input)
       } else {
         return .invalid(.notEmpty)
diff --git a/Tests/ValidationKitTests/EmptyTests.swift b/Tests/ValidationKitTests/EmptyTests.swift
index 636e9e2..c1d96a1 100644
--- a/Tests/ValidationKitTests/EmptyTests.swift
+++ b/Tests/ValidationKitTests/EmptyTests.swift
@@ -2,10 +2,11 @@ import XCTest
 import ValidationKit
 
 class EmptyTests: XCTestCase {
-  func testIsEmpty() {
+  func testIsEmptyNullable() {
     let validator = Validator<String?, String>.isEmpty
 
     // Valid
+    XCTAssertEqual(validator.validate(input: nil).value, "")
     XCTAssertEqual(validator.validate(input: "").value, "")
     XCTAssertEqual(validator.validate(input: " ").value, "")
 
@@ -14,7 +15,7 @@ class EmptyTests: XCTestCase {
     XCTAssertFalse(validator.validate(input: "F").isValid)
   }
 
-  func testNotEmpty() {
+  func testNotEmptyNullable() {
     let validator = Validator<String?, String>.notEmpty
 
     // Valid
@@ -22,6 +23,32 @@ class EmptyTests: XCTestCase {
     XCTAssertEqual(validator.validate(input: " F").value, "F")
     XCTAssertEqual(validator.validate(input: "F ").value, "F")
 
+    // Invalid
+    XCTAssertFalse(validator.validate(input: nil).isValid)
+    XCTAssertFalse(validator.validate(input: "").isValid)
+    XCTAssertFalse(validator.validate(input: " ").isValid)
+  }
+
+  func testIsEmpty() {
+    let validator = Validator<String, String>.isEmpty
+
+    // Valid
+    XCTAssertEqual(validator.validate(input: "").value, "")
+    XCTAssertEqual(validator.validate(input: " ").value, "")
+
+    // Invalid
+    XCTAssertFalse(validator.validate(input: "eerste etage").isValid)
+    XCTAssertFalse(validator.validate(input: "F").isValid)
+  }
+
+  func testNotEmpty() {
+    let validator = Validator<String, String>.notEmpty
+
+    // Valid
+    XCTAssertEqual(validator.validate(input: "eerste etage").value, "eerste etage")
+    XCTAssertEqual(validator.validate(input: " F").value, "F")
+    XCTAssertEqual(validator.validate(input: "F ").value, "F")
+
     // Invalid
     XCTAssertFalse(validator.validate(input: "").isValid)
     XCTAssertFalse(validator.validate(input: " ").isValid)