bug #4911 PhpdocSeparationFixer - fix regression with lack of next line (keradus)

This PR was submitted for the 2.16 branch but it was squashed and merged into the 2.15 branch instead (closes #4911).

Discussion
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PhpdocSeparationFixer - fix regression with lack of next line

Commits
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323c594 PhpdocSeparationFixer - fix regression with lack of next line

Author: keradus

src/Fixer/Phpdoc/PhpdocSeparationFixer.php

@@ -102,7 +102,7 @@ private function fixDescription(DocBlock $doc)
             if ($line->containsUsefulContent()) {
                 $next = $doc->getLine($index + 1);
 
-                if ($next->containsATag()) {
+                if (null !== $next && $next->containsATag()) {
                     $line->addBlank();
 
                     break;

tests/Fixer/Phpdoc/PhpdocSeparationFixerTest.php

@@ -573,6 +573,18 @@ public function testLargerEmptyDocBlock()
      *
      */
 
+EOF;
+
+        $this->doTest($expected);
+    }
+
+    public function testOneLineDocBlock()
+    {
+        $expected = <<<'EOF'
+<?php
+    /** Foo */
+    const Foo = 1;
+
 EOF;
 
         $this->doTest($expected);