don't fail if config path is unavailable

src/ConfigPaths.php

@@ -88,13 +88,16 @@ private function windowsHomeDir()
         return null;
     }
 
-    private function homeConfigDir()
+    private function homeConfigDir(): ?string
     {
         if ($homeConfigDir = $this->getEnv('XDG_CONFIG_HOME')) {
             return $homeConfigDir;
         }
 
         $homeDir = $this->homeDir();
+        if ($homeDir === null) {
+            return null;
+        }
 
         return $homeDir === '/' ? $homeDir.'.config' : $homeDir.'/.config';
     }
@@ -130,7 +133,7 @@ public function configDirs(): array
      *
      * @see self::homeConfigDir
      */
-    public function currentConfigDir(): string
+    public function currentConfigDir(): ?string
     {
         if ($this->configDir !== null) {
             return $this->configDir;
@@ -144,7 +147,7 @@ public function currentConfigDir(): string
             }
         }
 
-        return $configDirs[0];
+        return $configDirs[0] ?? null;
     }
 
     /**
@@ -259,6 +262,7 @@ public function which($command)
      */
     private function allDirNames(array $baseDirs): array
     {
+        $baseDirs = \array_filter($baseDirs);
         $dirs = \array_map(function ($dir) {
             return \strtr($dir, '\\', '/').'/psysh';
         }, $baseDirs);

src/Configuration.php

@@ -657,7 +657,7 @@ public function setHistoryFile(string $file)
      * Defaults to `/history` inside the shell's base config dir unless
      * explicitly overridden.
      */
-    public function getHistoryFile(): string
+    public function getHistoryFile(): ?string
     {
         if (isset($this->historyFile)) {
             return $this->historyFile;
@@ -674,6 +674,10 @@ public function getHistoryFile(): string
             $this->setHistoryFile($files[0]);
         } else {
             // fallback: create our own history file
+            $currentConfDir = $this->configPaths->currentConfigDir();
+            if ($currentConfDir === null) {
+                return null;
+            }
             $this->setHistoryFile($this->configPaths->currentConfigDir().'/psysh_history');
         }