changed tearDown function

Query/Span/SpanFirstQueryTest.php

@@ -43,7 +43,7 @@ class SpanFirstQueryTest extends \PHPUnit_Framework_TestCase
      */
     public function tearDown()
     {
-        $this->mock = null;
+        unset($this->mock);
     }
 
     /**

Query/Span/SpanMultiTermQueryTest.php

@@ -49,7 +49,7 @@ class SpanMultiTermQueryTest extends \PHPUnit_Framework_TestCase
      */
     public function tearDown()
     {
-        $this->mock = null;
+        unset($this->mock);
     }
 
     /**

Query/Span/SpanNearQueryTest.php

@@ -43,7 +43,7 @@ class SpanNearQueryTest extends \PHPUnit_Framework_TestCase
      */
     public function tearDown()
     {
-        $this->mock = null;
+        unset($this->mock);
     }
 
     /**

Query/Span/SpanNotQueryTest.php

@@ -43,7 +43,7 @@ class SpanNotQueryTest extends \PHPUnit_Framework_TestCase
      */
     public function tearDown()
     {
-        $this->mock = null;
+        unset($this->mock);
     }
 
     /**

Query/Span/SpanOrQueryTest.php

@@ -43,7 +43,7 @@ class SpanOrQueryTest extends \PHPUnit_Framework_TestCase
      */
     public function tearDown()
     {
-        $this->mock = null;
+        unset($this->mock);
     }
 
     /**