editor callback: allow to return empty value

src/Whoops/Handler/PrettyPageHandler.php

@@ -507,6 +507,10 @@ class PrettyPageHandler extends Handler
                 $callback = call_user_func($this->editors[$this->editor], $filePath, $line);
             }
 
+            if (empty($callback)) {
+                return [];
+            }
+
             if (is_string($callback)) {
                 return [
                     'ajax' => false,

tests/Whoops/Handler/PrettyPageHandlerTest.php

@@ -288,6 +288,14 @@ class PrettyPageHandlerTest extends TestCase
             false
         );
 
+        $handler->setEditor(function ($file, $line) {
+            return false;
+        });
+
+        $this->assertEquals(
+            $handler->getEditorHref('/foo/bar.php', 10),
+            false
+        );
     }
 
     /**