diff --git a/src/RecipeCommandBehaviour.php b/src/RecipeCommandBehaviour.php
index 8354ac5..3ee5c04 100644
--- a/src/RecipeCommandBehaviour.php
+++ b/src/RecipeCommandBehaviour.php
@@ -103,17 +103,17 @@ protected function findBestConstraint($existingVersion)
         }
 
         // Existing version is already a ^1.0.0 or ~1.0.0 constraint
-        if (preg_match('#^[~^]#', $existingVersion)) {
+        if (preg_match('#^[~^]#', $existingVersion ?? '')) {
             return $existingVersion;
         }
 
         // Existing version is already a dev constraint
-        if (stristr($existingVersion, 'dev') !== false) {
+        if (stristr($existingVersion ?? '', 'dev') !== false) {
             return $existingVersion;
         }
 
         // Numeric-only version maps to semver constraint
-        if (preg_match('#^([\d.]+)$#', $existingVersion)) {
+        if (preg_match('#^([\d.]+)$#', $existingVersion ?? '')) {
             return "^{$existingVersion}";
         }
 
diff --git a/src/RecipeInstaller.php b/src/RecipeInstaller.php
index 767c660..5889094 100644
--- a/src/RecipeInstaller.php
+++ b/src/RecipeInstaller.php
@@ -61,7 +61,7 @@ protected function installProjectFiles(
             $relativePath = $this->installProjectFile($sourceRoot, $destinationRoot, $path, $installedFiles);
 
             // Add file to installed (even if already exists)
-            if (!in_array($relativePath, $installedFiles)) {
+            if (!in_array($relativePath, $installedFiles ?? [])) {
                 $installedFiles[] = $relativePath;
             }
         }
@@ -87,15 +87,15 @@ protected function installProjectFiles(
     protected function installProjectFile($sourceRoot, $destinationRoot, $sourcePath, $installedFiles)
     {
         // Relative path
-        $relativePath = substr($sourcePath, strlen($sourceRoot) + 1); // Name path without leading '/'
+        $relativePath = substr($sourcePath ?? '', strlen($sourceRoot ?? '') + 1); // Name path without leading '/'
 
         // Get destination path
         $relativeDestination = $this->rewriteFilePath($destinationRoot, $relativePath);
         $destination = $destinationRoot . DIRECTORY_SEPARATOR . $relativeDestination;
 
         // Check if file exists
-        if (file_exists($destination)) {
-            if (file_get_contents($destination) === file_get_contents($sourcePath)) {
+        if (file_exists($destination ?? '')) {
+            if (file_get_contents($destination ?? '') === file_get_contents($sourcePath ?? '')) {
                 $this->io->write(
                     "  - Skipping <info>$relativePath</info> (<comment>existing, but unchanged</comment>)"
                 );
@@ -104,15 +104,17 @@ protected function installProjectFile($sourceRoot, $destinationRoot, $sourcePath
                     "  - Skipping <info>$relativePath</info> (<comment>existing and modified in project</comment>)"
                 );
             }
-        } elseif (in_array($relativePath, $installedFiles) || in_array($relativeDestination, $installedFiles)) {
+        } elseif (in_array($relativePath, $installedFiles ?? []) ||
+            in_array($relativeDestination, $installedFiles ?? [])
+        ) {
             // Don't re-install previously installed files that have been deleted
             $this->io->write(
                 "  - Skipping <info>$relativePath</info> (<comment>previously installed</comment>)"
             );
         } else {
             $this->io->write("  - Copying <info>$relativePath</info>");
-            $this->filesystem->ensureDirectoryExists(dirname($destination));
-            copy($sourcePath, $destination);
+            $this->filesystem->ensureDirectoryExists(dirname($destination ?? ''));
+            copy($sourcePath ?? '', $destination ?? '');
         }
         return $relativePath;
     }
@@ -155,10 +157,10 @@ protected function getFileIterator($sourceRoot, $patterns)
      */
     protected function globToRegexp($glob)
     {
-        $sourceParts = explode('*', $glob);
+        $sourceParts = explode('*', $glob ?? '');
         $regexParts = array_map(function ($part) {
-            return preg_quote($part, '#');
-        }, $sourceParts);
+            return preg_quote($part ?? '', '#');
+        }, $sourceParts ?? []);
         return implode('(.+)', $regexParts);
     }
 
@@ -176,11 +178,11 @@ public function installLibrary(PackageInterface $package)
         $recipePath = $this->getInstallPath($package);
 
         // Find project path
-        $projectPath = dirname(realpath(Factory::getComposerFile()));
+        $projectPath = dirname(realpath(Factory::getComposerFile() ?? '') ?? '');
 
         // Find public path
         $candidatePublicPath = $projectPath . DIRECTORY_SEPARATOR . RecipePlugin::PUBLIC_PATH;
-        $publicPath = is_dir($candidatePublicPath) ? $candidatePublicPath : $projectPath;
+        $publicPath = is_dir($candidatePublicPath ?? '') ? $candidatePublicPath : $projectPath;
 
         // Copy project files to root
         $name = $package->getName();
@@ -238,8 +240,8 @@ protected function rewriteFilePath($destinationRoot, $relativePath)
             'app' => 'mysite',
         ];
         foreach ($rewrites as $from => $to) {
-            if (stripos($relativePath, $from) === 0) {
-                return $to . substr($relativePath, strlen($from));
+            if (stripos($relativePath ?? '', $from ?? '') === 0) {
+                return $to . substr($relativePath ?? '', strlen($from ?? ''));
             }
         }
         return $relativePath;
diff --git a/src/RecipePlugin.php b/src/RecipePlugin.php
index ecdc3fe..fd65c3c 100644
--- a/src/RecipePlugin.php
+++ b/src/RecipePlugin.php
@@ -137,11 +137,9 @@ public function getCapabilities()
 
     public function deactivate(Composer $composer, IOInterface $io)
     {
-
     }
 
     public function uninstall(Composer $composer, IOInterface $io)
     {
-
     }
 }