diff --git a/CHANGELOG.md b/CHANGELOG.md
index 035502d..927a9c3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed
+- `ReCaptchaTrait::validateReCaptchaFromRequest()` treats a missing or empty
+  `g-recaptcha-response` as an invalid captcha (returns `false`) instead of passing `null` to the
+  non-nullable `validateReCaptcha(string ...)`, which raised a `TypeError` (HTTP 500). A tokenless
+  request — e.g. a programmatic JSON client — now fails the reCaptcha check cleanly.
 
 ## [10.1.2] - 2025-09-26
 - Github social login
diff --git a/src/Traits/ReCaptchaTrait.php b/src/Traits/ReCaptchaTrait.php
index be4bba8..0cc2b20 100644
--- a/src/Traits/ReCaptchaTrait.php
+++ b/src/Traits/ReCaptchaTrait.php
@@ -36,7 +36,13 @@ public function validateReCaptchaFromRequest(ServerRequestInterface $request): b
             throw new BadMethodCallException('Request must be an instance of ServerRequest');
         }
         $data = $request->getParsedBody();
-        $captcha = $data['g-recaptcha-response'] ?? null;
+        $captcha = is_array($data) ? ($data['g-recaptcha-response'] ?? null) : null;
+        // A missing/empty token is simply an invalid captcha. Guard here so a request
+        // without the field (e.g. a programmatic JSON client) fails validation cleanly
+        // instead of hitting validateReCaptcha()'s non-nullable string param (TypeError -> 500).
+        if (!is_string($captcha) || $captcha === '') {
+            return false;
+        }
 
         return $this->validateReCaptcha(
             $captcha,
diff --git a/tests/TestCase/Authenticator/FormAuthenticatorTest.php b/tests/TestCase/Authenticator/FormAuthenticatorTest.php
index 9e30092..5843c54 100644
--- a/tests/TestCase/Authenticator/FormAuthenticatorTest.php
+++ b/tests/TestCase/Authenticator/FormAuthenticatorTest.php
@@ -299,6 +299,66 @@ public function testAuthenticateInvalidRecaptcha()
         $this->assertNull($result->getData());
     }
 
+    /**
+     * A request without a g-recaptcha-response token, with reCaptcha enabled and valid
+     * credentials, must fail as FAILURE_INVALID_RECAPTCHA through the real
+     * validateReCaptchaFromRequest() guard (no token never reaches validateReCaptcha(),
+     * so this asserts the guard end-to-end and that it no longer raises a TypeError).
+     *
+     * @return void
+     */
+    public function testAuthenticateTokenlessRecaptchaFailsCleanly()
+    {
+        $identifiers = new IdentifierCollection([
+            'Authentication.Password',
+        ]);
+
+        $BaseAuthenticator = $this->getMockBuilder(CakeFormAuthenticator::class)
+            ->setConstructorArgs([$identifiers])
+            ->onlyMethods(['authenticate'])
+            ->getMock();
+        $request = ServerRequestFactory::fromGlobals(
+            ['REQUEST_URI' => '/testpath', 'REMOTE_ADDR' => '127.0.0.1'],
+            [],
+            ['username' => 'marcelo', 'password' => 'password']
+        );
+
+        $baseResult = new Result(
+            [
+                'id' => '42',
+                'username' => 'marcelo',
+                'role' => 'user',
+            ],
+            Result::SUCCESS
+        );
+        $BaseAuthenticator->expects($this->once())
+            ->method('authenticate')
+            ->with($request)
+            ->will($this->returnValue($baseResult));
+
+        // Only the base authenticator is mocked; validateReCaptcha() is left real and
+        // must never be reached because the token is absent.
+        $Authenticator = $this->getMockBuilder(FormAuthenticator::class)->setConstructorArgs([
+            $identifiers,
+            [
+                'fields' => [
+                    AbstractIdentifier::CREDENTIAL_USERNAME => 'email',
+                    AbstractIdentifier::CREDENTIAL_PASSWORD => 'password',
+                ],
+            ],
+        ])->onlyMethods(['createBaseAuthenticator'])->getMock();
+
+        Configure::write('Users.reCaptcha.login', true);
+        $Authenticator->expects($this->once())
+            ->method('createBaseAuthenticator')
+            ->will($this->returnValue($BaseAuthenticator));
+
+        $result = $Authenticator->authenticate($request);
+        $this->assertInstanceOf(Result::class, $result);
+        $this->assertEquals(FormAuthenticator::FAILURE_INVALID_RECAPTCHA, $result->getStatus());
+        $this->assertNull($result->getData());
+    }
+
     /**
      * test getBaseAuthenticator
      *
diff --git a/tests/TestCase/Traits/ReCaptchaTraitTest.php b/tests/TestCase/Traits/ReCaptchaTraitTest.php
new file mode 100644
index 0000000..b214e92
--- /dev/null
+++ b/tests/TestCase/Traits/ReCaptchaTraitTest.php
@@ -0,0 +1,111 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * Copyright 2010 - 2026, Cake Development Corporation (https://www.cakedc.com)
+ *
+ * Licensed under The MIT License
+ * Redistributions of files must retain the above copyright notice.
+ *
+ * @copyright Copyright 2010 - 2026, Cake Development Corporation (https://www.cakedc.com)
+ * @license MIT License (http://www.opensource.org/licenses/mit-license.php)
+ */
+
+namespace CakeDC\Auth\Test\TestCase\Traits;
+
+use Cake\Http\ServerRequest;
+use Cake\Http\ServerRequestFactory;
+use Cake\TestSuite\TestCase;
+use CakeDC\Auth\Traits\ReCaptchaTrait;
+
+class ReCaptchaTraitTest extends TestCase
+{
+    protected function request(mixed $parsedBody): ServerRequest
+    {
+        /** @var \Cake\Http\ServerRequest $request */
+        $request = ServerRequestFactory::fromGlobals(['REMOTE_ADDR' => '127.0.0.1']);
+
+        return $request->withParsedBody($parsedBody);
+    }
+
+    /**
+     * A subject that uses the trait and stubs the actual verification so the tests
+     * never reach _getReCaptchaInstance()/the google/recaptcha dependency and can
+     * observe whether the guard short-circuited.
+     *
+     * @param bool $return value the stubbed validateReCaptcha() returns
+     * @return object
+     */
+    protected function subject(bool $return = true): object
+    {
+        return new class ($return) {
+            use ReCaptchaTrait;
+
+            public bool $validatorCalled = false;
+            public array $validatorArgs = [];
+
+            public function __construct(protected bool $return)
+            {
+            }
+
+            public function validateReCaptcha(string $recaptchaResponse, string $clientIp): bool
+            {
+                $this->validatorCalled = true;
+                $this->validatorArgs = [$recaptchaResponse, $clientIp];
+
+                return $this->return;
+            }
+        };
+    }
+
+    /**
+     * @return array<string, array{0: mixed}>
+     */
+    public static function tokenlessProvider(): array
+    {
+        return [
+            'missing field' => [[]],
+            'empty string' => [['g-recaptcha-response' => '']],
+            'array value' => [['g-recaptcha-response' => ['nested']]],
+            'object body' => [(object)['g-recaptcha-response' => 'x']],
+        ];
+    }
+
+    /**
+     * A missing/empty/non-string token is invalid and must not reach the verifier.
+     *
+     * @dataProvider tokenlessProvider
+     * @param mixed $parsedBody parsed request body
+     * @return void
+     */
+    public function testTokenlessRequestFailsWithoutCallingValidator(mixed $parsedBody): void
+    {
+        $subject = $this->subject(true);
+
+        $result = $subject->validateReCaptchaFromRequest($this->request($parsedBody));
+
+        $this->assertFalse($result);
+        $this->assertFalse(
+            $subject->validatorCalled,
+            'The guard must short-circuit before validateReCaptcha().',
+        );
+    }
+
+    /**
+     * A real token is forwarded verbatim to validateReCaptcha() with the client IP.
+     *
+     * @return void
+     */
+    public function testValidTokenDelegatesToValidator(): void
+    {
+        $subject = $this->subject(true);
+
+        $result = $subject->validateReCaptchaFromRequest(
+            $this->request(['g-recaptcha-response' => 'the-token']),
+        );
+
+        $this->assertTrue($result);
+        $this->assertTrue($subject->validatorCalled);
+        $this->assertSame(['the-token', '127.0.0.1'], $subject->validatorArgs);
+    }
+}