Fix inconsistent return points.

Author: derrabus

Pipes/AbstractPipes.php

@@ -88,12 +88,14 @@ protected function unblock()
     /**
      * Writes input to stdin.
      *
+     * @return array|null
+     *
      * @throws InvalidArgumentException When an input iterator yields a non supported value
      */
     protected function write()
     {
         if (!isset($this->pipes[0])) {
-            return;
+            return null;
         }
         $input = $this->input;
 
@@ -122,7 +124,7 @@ protected function write()
 
         // let's have a look if something changed in streams
         if (false === @stream_select($r, $w, $e, 0, 0)) {
-            return;
+            return null;
         }
 
         foreach ($w as $stdin) {
@@ -166,6 +168,8 @@ protected function write()
         } elseif (!$w) {
             return [$this->pipes[0]];
         }
+
+        return null;
     }
 
     /**

Tests/ProcessTest.php

@@ -1231,6 +1231,8 @@ public function testInputStreamWithCallable()
 
                 return $stream;
             }
+
+            return null;
         };
 
         $input = new InputStream();