feat: add workround for implicit nullable deprecation errors in PHP 8.4

Author: kenjis

system/Debug/Exceptions.php

@@ -213,6 +213,10 @@ public function errorHandler(int $severity, string $message, ?string $file = nul
                 return true;
             }
 
+            if ($this->isImplicitNullableDeprecationError($message, $file, $line)) {
+                return true;
+            }
+
             if (! $this->config->logDeprecations || (bool) env('CODEIGNITER_SCREAM_DEPRECATIONS')) {
                 throw new ErrorException($message, 0, $severity, $file, $line);
             }
@@ -253,6 +257,34 @@ private function isSessionSidDeprecationError(string $message, ?string $file = n
         return false;
     }
 
+    /**
+     * Workaround to implicit nullable deprecation errors in PHP 8.4.
+     *
+     * "Implicitly marking parameter $xxx as nullable is deprecated,
+     *  the explicit nullable type must be used instead"
+     */
+    private function isImplicitNullableDeprecationError(string $message, ?string $file = null, ?int $line = null): bool
+    {
+        if (
+            PHP_VERSION_ID >= 80400
+            && str_contains($message, 'the explicit nullable type must be used instead')
+        ) {
+            log_message(
+                LogLevel::WARNING,
+                '[DEPRECATED] {message} in {errFile} on line {errLine}.',
+                [
+                    'message' => $message,
+                    'errFile' => clean_path($file ?? ''),
+                    'errLine' => $line ?? 0,
+                ]
+            );
+
+            return true;
+        }
+
+        return false;
+    }
+
     /**
      * Checks to see if any errors have happened during shutdown that
      * need to be caught and handle them.