Replaced array_walk() with foreach().

Add a more detailed exception message when a top-level key is missing.

Fixed style in README.md.

Processor.php

@@ -33,7 +33,7 @@ public function processFile(array $config)
         // Find the expected params
         $expectedValues = $yamlParser->parse(file_get_contents($config['dist-file']));
         if (!isset($expectedValues[$parameterKey])) {
-            throw new \InvalidArgumentException('The dist file seems invalid.');
+            throw new \InvalidArgumentException(sprintf('The top-level key %s is missing.', $parameterKey));
         }
         $expectedParams = (array) $expectedValues[$parameterKey];
 
@@ -104,9 +104,9 @@ private function processParams(array $config, array $expectedParams, array $actu
         if (!empty($config['env-map'])) {
             // Hydrate env-map from dist file
             if ('auto' === $config['env-map']) {
-                array_walk($expectedParams, function($v, $k) use (&$envMap) {
-                    $envMap[$k] = strtoupper($k);
-                });
+                foreach ($expectedParams as $key => $value) {
+                    $envMap[$key] = strtoupper($key);
+                }
             } else {
                 $envMap = (array) $config['env-map'];
             }

README.md

@@ -122,7 +122,7 @@ As environment variables can only be strings, they are also parsed as inline
 Yaml values to allows specifying ``null``, ``false``, ``true`` or numbers
 easily.
 
-## Using same names for parameters and environment variables
+#### Using same names for parameters and environment variables
 
 As an alternative, you can set environment variables with the same uppercased
 name of your dist parameters and use ``"env-map": "auto"`` to get an auto mapping.

Tests/ProcessorTest.php

@@ -74,7 +74,7 @@ public function provideInvalidConfiguration()
                 array(
                     'file' => 'fixtures/invalid/missing_top_level.yml',
                 ),
-                'The dist file seems invalid.',
+                'The top-level key parameters is missing.',
             ),
             'invalid values in the existing file' => array(
                 array(