diff --git a/src/Console/Commands/Compose.php b/src/Console/Commands/Compose.php
index aad21e6..2a9b762 100644
--- a/src/Console/Commands/Compose.php
+++ b/src/Console/Commands/Compose.php
@@ -22,7 +22,14 @@ class Compose extends Command
 
     public function __construct()
     {
-        $this->workingDir = getcwd();
+        $workingDir = getcwd();
+
+        if (! $workingDir) {
+            throw new Exception('Unable to determine the working directory.');
+        }
+
+        $this->workingDir = $workingDir;
+
         parent::__construct();
     }
 
diff --git a/src/Mover.php b/src/Mover.php
index 4f3d65d..8b676be 100644
--- a/src/Mover.php
+++ b/src/Mover.php
@@ -73,7 +73,7 @@ private function deleteDepTargetDirs(Package $package): void
             switch ($autoloaderType) {
                 case Psr0::class:
                 case Psr4::class:
-                    $outputDir = $this->config->getDepDirectory() . $packageAutoloader->namespace;
+                    $outputDir = $this->config->getDepDirectory() . $packageAutoloader->getSearchNamespace();
                     $outputDir = str_replace('\\', DIRECTORY_SEPARATOR, $outputDir);
                     $this->filesystem->deleteDirectory($outputDir);
                     break;
diff --git a/src/Replace/ClassmapReplacer.php b/src/Replace/ClassmapReplacer.php
index 41323fa..39b4fa5 100644
--- a/src/Replace/ClassmapReplacer.php
+++ b/src/Replace/ClassmapReplacer.php
@@ -6,6 +6,8 @@
 
 namespace CoenJacobs\Mozart\Replace;
 
+use Exception;
+
 class ClassmapReplacer extends BaseReplacer
 {
 
@@ -15,16 +17,13 @@ class ClassmapReplacer extends BaseReplacer
     /** @var string */
     public $classmap_prefix;
 
-    /**
-     * @param false|string $contents
-     */
-    public function replace($contents): string
+    public function replace(string $contents): string
     {
-        if (empty($contents) || false === $contents) {
+        if (empty($contents)) {
             return '';
         }
 
-        return preg_replace_callback(
+        $replaced = preg_replace_callback(
             "
 			/													# Start the pattern
 						namespace\s+[a-zA-Z0-9_\x7f-\xff\\\\]+[;{\s\n]{1}.*?(?=namespace|$)
@@ -39,7 +38,7 @@ public function replace($contents): string
 						(?:{|extends|implements|\n)				# Class declaration can be followed by {, extends,
 																# implements, or a new line
 			/sx", //                                            # dot matches newline, ignore whitespace in regex.
-            function ($matches) use ($contents) {
+            function ($matches) {
 
                 // If we're inside a namespace other than the global namesspace, just return.
                 if (preg_match('/^namespace\s+[a-zA-Z0-9_\x7f-\xff\\\\]+[;{\s\n]{1}.*/', $matches[0])) {
@@ -53,9 +52,15 @@ function ($matches) use ($contents) {
             },
             $contents
         );
+
+        if (empty($replaced)) {
+            throw new Exception('Failed to replace contents of the file.');
+        }
+
+        return $replaced;
     }
 
-    public function saveReplacedClass($classname, string $replacedName): void
+    public function saveReplacedClass(string $classname, string $replacedName): void
     {
         $this->replacedClasses[ $classname ] = $replacedName;
     }
diff --git a/src/Replace/NamespaceReplacer.php b/src/Replace/NamespaceReplacer.php
index 680fb41..b348fb2 100644
--- a/src/Replace/NamespaceReplacer.php
+++ b/src/Replace/NamespaceReplacer.php
@@ -2,6 +2,8 @@
 
 namespace CoenJacobs\Mozart\Replace;
 
+use Exception;
+
 class NamespaceReplacer extends BaseReplacer
 {
     /**
@@ -15,12 +17,12 @@ class NamespaceReplacer extends BaseReplacer
      * @param string $contents The text to make replacements in.
      * @param null $file Only used in ClassmapReplacer (for recording which files were changed).
      */
-    public function replace($contents, $file = null): string
+    public function replace(string $contents, string $file = null): string
     {
         $searchNamespace = preg_quote($this->autoloader->getSearchNamespace(), '/');
         $dependencyNamespace = preg_quote($this->dep_namespace, '/');
 
-        return preg_replace_callback(
+        $replaced = preg_replace_callback(
             "
             /                                # Start the pattern
               ([^a-zA-Z0-9_\x7f-\xff])       # Match the non-class character before the namespace
@@ -37,5 +39,11 @@ function ($matches) {
             },
             $contents
         );
+
+        if (empty($replaced)) {
+            throw new Exception('Failed to replace contents of the file.');
+        }
+
+        return $replaced;
     }
 }
diff --git a/src/Replace/Replacer.php b/src/Replace/Replacer.php
index 33b1a15..907bdf9 100644
--- a/src/Replace/Replacer.php
+++ b/src/Replace/Replacer.php
@@ -6,6 +6,6 @@
 
 interface Replacer
 {
-    public function setAutoloader(Autoloader $autoloader);
-    public function replace($contents);
+    public function setAutoloader(Autoloader $autoloader): void;
+    public function replace(string $contents): string;
 }
diff --git a/src/Replacer.php b/src/Replacer.php
index bc2668b..c092bcf 100644
--- a/src/Replacer.php
+++ b/src/Replacer.php
@@ -9,6 +9,7 @@
 use CoenJacobs\Mozart\Config\Package;
 use CoenJacobs\Mozart\Replace\ClassmapReplacer;
 use CoenJacobs\Mozart\Replace\NamespaceReplacer;
+use Exception;
 use League\Flysystem\Local\LocalFilesystemAdapter;
 use League\Flysystem\UnableToReadFile;
 use League\Flysystem\Filesystem;
@@ -25,7 +26,7 @@ class Replacer
     /** @var Mozart */
     protected $config;
 
-    /** @var array */
+    /** @var array<string,string> */
     protected $replacedClasses = [];
 
     /** @var Filesystem */
@@ -48,7 +49,7 @@ public function __construct(string $workingDir, Mozart $config)
     /**
      * @param Package[] $packages
      */
-    public function replacePackages($packages): void
+    public function replacePackages(array $packages): void
     {
         foreach ($packages as $package) {
             $this->replacePackages($package->getDependencies());
@@ -141,10 +142,6 @@ public function replaceParentClassesInDirectory(string $directory): void
                     continue;
                 }
 
-                if (!$contents) {
-                    continue;
-                }
-
                 foreach ($replacedClasses as $original => $replacement) {
                     $contents = preg_replace_callback(
                         '/(.*)([^a-zA-Z0-9_\x7f-\xff])'. $original . '([^a-zA-Z0-9_\x7f-\xff])/U',
@@ -156,10 +153,10 @@ function ($matches) use ($replacement) {
                         },
                         $contents
                     );
-                }
 
-                if (empty($contents)) {
-                    continue;
+                    if (empty($contents)) {
+                        throw new Exception('Failed to replace parent classes in directory.');
+                    }
                 }
 
                 $this->filesystem->write($targetFile, $contents);