diff --git a/composer.json b/composer.json
index b996cc2..f273ba1 100644
--- a/composer.json
+++ b/composer.json
@@ -77,7 +77,7 @@
             "@php bin/cli orm:clear-cache:result --flush"
         ],
         "doctrine:initialize-database": [
-            "@php bin/cli orm:schema-tool:update --complete --force",
+            "@php bin/cli orm:schema-tool:update --force",
             "@php bin/cli oai:formats:update --quiet"
         ],
         "php-cs-fixer:check": [
diff --git a/config/config.dist.yml b/config/config.dist.yml
index 0017c78..bbcf2f3 100644
--- a/config/config.dist.yml
+++ b/config/config.dist.yml
@@ -21,8 +21,8 @@ adminEmail: 'admin@example.org'
 #
 # Database connection details
 #
-# This has to be a valid data source name (DSN) URL. The scheme is used to
-# specify a driver, the user and password in the URL encode user and password
+# This has to be a valid data source name (DSN) URI. The scheme is used to
+# specify a driver, the user and password in the URI encode user and password
 # for the connection, followed by the host and port parts. The path after the
 # authority part represents the name of the database (the leading slash is
 # removed so add an extra slash to specify an absolute file path for SQLite).
diff --git a/src/Configuration.php b/src/Configuration.php
index 30cbab6..d69d651 100644
--- a/src/Configuration.php
+++ b/src/Configuration.php
@@ -130,7 +130,8 @@ class Configuration
      *
      * @return array<TKey, TValue> The configuration array
      *
-     * @throws FileNotFoundException|ValidationFailedException
+     * @throws FileNotFoundException if configuration file does not exist
+     * @throws ValidationFailedException if configuration file is not valid
      */
     protected function loadConfigFile(): array
     {
@@ -159,7 +160,8 @@ class Configuration
     /**
      * Load and validate configuration settings from YAML file.
      *
-     * @throws FileNotFoundException | ValidationFailedException
+     * @throws FileNotFoundException if configuration file does not exist
+     * @throws ValidationFailedException if configuration file is not valid
      */
     private function __construct()
     {
diff --git a/src/Middleware.php b/src/Middleware.php
index 10e8c56..8ca7538 100644
--- a/src/Middleware.php
+++ b/src/Middleware.php
@@ -78,6 +78,9 @@ abstract class Middleware extends AbstractMiddleware
         return $response;
     }
 
+    /**
+     * The constructor must have the same signature for all derived classes, thus make it final.
+     */
     final public function __construct()
     {
         // Make constructor final to avoid issues in dispatcher.
diff --git a/src/Middleware/Dispatcher.php b/src/Middleware/Dispatcher.php
index 1259088..101272e 100644
--- a/src/Middleware/Dispatcher.php
+++ b/src/Middleware/Dispatcher.php
@@ -85,7 +85,8 @@ class Dispatcher extends AbstractMiddleware
     protected function processRequest(ServerRequestInterface $request): ServerRequestInterface
     {
         $request = $this->getRequestWithAttributes($request);
-        if (!ErrorHandler::getInstance()->hasErrors()) {
+        $errorHandler = ErrorHandler::getInstance();
+        if (!$errorHandler->hasErrors()) {
             /** @var string */
             $verb = $request->getAttribute('verb');
             $middleware = __NAMESPACE__ . '\\' . $verb;
@@ -93,7 +94,7 @@ class Dispatcher extends AbstractMiddleware
                 $this->requestHandler->queue->enqueue(new $middleware());
             }
         }
-        $this->requestHandler->queue->enqueue(ErrorHandler::getInstance());
+        $this->requestHandler->queue->enqueue($errorHandler);
         return $request;
     }
 
@@ -114,6 +115,7 @@ class Dispatcher extends AbstractMiddleware
 
     /**
      * Validate the request parameters.
+     *
      * @see https://openarchives.org/OAI/openarchivesprotocol.html#ProtocolMessages
      *
      * @param string[] $arguments The request parameters
@@ -122,11 +124,12 @@ class Dispatcher extends AbstractMiddleware
      */
     protected function validateArguments(array $arguments): bool
     {
+        $errorHandler = ErrorHandler::getInstance();
         if (
             count(array_diff(array_keys($arguments), self::OAI_PARAMS)) !== 0
             or !isset($arguments['verb'])
         ) {
-            ErrorHandler::getInstance()->withError('badArgument');
+            $errorHandler->withError('badArgument');
         } else {
             switch ($arguments['verb']) {
                 case 'GetRecord':
@@ -135,12 +138,12 @@ class Dispatcher extends AbstractMiddleware
                         or !isset($arguments['identifier'])
                         or !isset($arguments['metadataPrefix'])
                     ) {
-                        ErrorHandler::getInstance()->withError('badArgument');
+                        $errorHandler->withError('badArgument');
                     }
                     break;
                 case 'Identify':
                     if (count($arguments) !== 1) {
-                        ErrorHandler::getInstance()->withError('badArgument');
+                        $errorHandler->withError('badArgument');
                     }
                     break;
                 case 'ListIdentifiers':
@@ -153,30 +156,30 @@ class Dispatcher extends AbstractMiddleware
                             (isset($arguments['resumptionToken']) && count($arguments) !== 2)
                             or isset($arguments['identifier'])
                         ) {
-                            ErrorHandler::getInstance()->withError('badArgument');
+                            $errorHandler->withError('badArgument');
                         }
                     } else {
-                        ErrorHandler::getInstance()->withError('badArgument');
+                        $errorHandler->withError('badArgument');
                     }
                     break;
                 case 'ListMetadataFormats':
                     if (count($arguments) !== 1) {
                         if (!isset($arguments['identifier']) || count($arguments) !== 2) {
-                            ErrorHandler::getInstance()->withError('badArgument');
+                            $errorHandler->withError('badArgument');
                         }
                     }
                     break;
                 case 'ListSets':
                     if (count($arguments) !== 1) {
                         if (!isset($arguments['resumptionToken']) || count($arguments) !== 2) {
-                            ErrorHandler::getInstance()->withError('badArgument');
+                            $errorHandler->withError('badArgument');
                         }
                     }
                     break;
                 default:
-                    ErrorHandler::getInstance()->withError('badVerb');
+                $errorHandler->withError('badVerb');
             }
         }
-        return !ErrorHandler::getInstance()->hasErrors();
+        return !$errorHandler->hasErrors();
     }
 }
diff --git a/src/Middleware/ErrorHandler.php b/src/Middleware/ErrorHandler.php
index ce28f43..129ebf5 100644
--- a/src/Middleware/ErrorHandler.php
+++ b/src/Middleware/ErrorHandler.php
@@ -42,6 +42,7 @@ class ErrorHandler extends AbstractMiddleware
 
     /**
      * List of defined OAI-PMH errors.
+     *
      * @see https://openarchives.org/OAI/openarchivesprotocol.html#ErrorConditions
      */
     protected const OAI_ERRORS = [
@@ -109,7 +110,7 @@ class ErrorHandler extends AbstractMiddleware
      *
      * @return ErrorHandler The ErrorHandler instance
      *
-     * @throws DomainException
+     * @throws DomainException if error code is not a valid OAI-PMH error
      */
     public function withError(string $errorCode): ErrorHandler
     {