[Process] Do not throw LogicException in ProcessBuilder::getProcess if no arguments are set but a prefix is

src/Symfony/Component/Process/ProcessBuilder.php

@@ -154,7 +154,7 @@ class ProcessBuilder
 
     public function getProcess()
     {
-        if (!count($this->arguments)) {
+        if (!$this->prefix && !count($this->arguments)) {
             throw new LogicException('You must add() command arguments before calling getProcess().');
         }
 

src/Symfony/Component/Process/Tests/ProcessBuilderTest.php

@@ -152,4 +152,29 @@ class ProcessBuilderTest extends \PHPUnit_Framework_TestCase
             $this->assertSame("'%prefix%' 'arg'", $proc->getCommandLine());
         }
     }
+
+    /**
+     * @expectedException \Symfony\Component\Process\Exception\LogicException
+     */
+    public function testShouldThrowALogicExceptionIfNoPrefixAndNoArgument()
+    {
+        ProcessBuilder::create()->getProcess();
+    }
+
+    public function testShouldNotThrowALogicExceptionIfNoArgument()
+    {
+        $process = ProcessBuilder::create()
+            ->setPrefix('/usr/bin/php')
+            ->getProcess();
+
+        $this->assertEquals("'/usr/bin/php'", $process->getCommandLine());
+    }
+
+    public function testShouldNotThrowALogicExceptionIfNoPrefix()
+    {
+        $process = ProcessBuilder::create(array('/usr/bin/php'))
+            ->getProcess();
+
+        $this->assertEquals("'/usr/bin/php'", $process->getCommandLine());
+    }
 }