fix: cast null to array before passing to array_merge() (#666)

Fixes #595

Author: netjan

src/Indexer.php

@@ -147,7 +147,7 @@ public function index(): Promise
                 $packageKey = null;
                 $cacheKey = null;
                 $index = null;
-                foreach (array_merge($this->composerLock->packages, $this->composerLock->{'packages-dev'}) as $package) {
+                foreach (array_merge($this->composerLock->packages, (array)$this->composerLock->{'packages-dev'}) as $package) {
                     // Check if package name matches and version is absolute
                     // Dynamic constraints are not cached, because they can change every time
                     $packageVersion = ltrim($package->version, 'v');

src/Server/Workspace.php

@@ -169,7 +169,7 @@ public function xdependencies(): array
             return [];
         }
         $dependencyReferences = [];
-        foreach (array_merge($this->composerLock->packages, $this->composerLock->{'packages-dev'}) as $package) {
+        foreach (array_merge($this->composerLock->packages, (array)$this->composerLock->{'packages-dev'}) as $package) {
             $dependencyReferences[] = new DependencyReference($package);
         }
         return $dependencyReferences;