[ErrorHandler] Fix strpos error when trying to call a method without a name

FatalErrorHandler/UndefinedMethodFatalErrorHandler.php

@@ -40,7 +40,7 @@ class UndefinedMethodFatalErrorHandler implements FatalErrorHandlerInterface
 
         $message = sprintf('Attempted to call an undefined method named "%s" of class "%s".', $methodName, $className);
 
-        if (!class_exists($className) || null === $methods = get_class_methods($className)) {
+        if ('' === $methodName || !class_exists($className) || null === $methods = get_class_methods($className)) {
             // failed to get the class or its methods on which an unknown method was called (for example on an anonymous class)
             return new UndefinedMethodException($message, $exception);
         }

Tests/FatalErrorHandler/UndefinedMethodFatalErrorHandlerTest.php

@@ -48,6 +48,15 @@ class UndefinedMethodFatalErrorHandlerTest extends TestCase
                 ],
                 'Attempted to call an undefined method named "what" of class "SplObjectStorage".',
             ],
+            [
+                [
+                    'type' => 1,
+                    'line' => 12,
+                    'file' => 'foo.php',
+                    'message' => 'Call to undefined method SplObjectStorage::()',
+                ],
+                'Attempted to call an undefined method named "" of class "SplObjectStorage".',
+            ],
             [
                 [
                     'type' => 1,