update: update some for cmd build

Author: inhere

src/Cmd/AbstractCmdBuilder.php

@@ -240,7 +240,10 @@ public function getWorkDir(): string
      */
     public function setWorkDir(string $workDir): static
     {
-        Assert::isDir($workDir, "workdir is not exists. path: $workDir");
+        if ($workDir) {
+            Assert::isDir($workDir, "workdir is not exists. path: $workDir");
+        }
+
         $this->workDir = $workDir;
         return $this;
     }

src/Cmd/CmdBuilder.php

@@ -131,6 +131,29 @@ public function addArgs(...$args): static
         return $this;
     }
 
+    /**
+     * Call fn on args is not empty.
+     *
+     * Usage:
+     *
+     * ```php
+     * $c->withIf(fn($args) => $c->addArgs(...$args), $args)
+     * ```
+     *
+     * @template T
+     * @param callable(T): void $fn
+     * @param T $args
+     *
+     * @return $this
+     */
+    public function withIf(callable $fn, mixed $args): static
+    {
+        if ($args) {
+            $fn($this);
+        }
+        return $this;
+    }
+
     /**
      * @param bool $printOutput
      *