Only send header when there is a value, fixes #352

src/Monolog/Handler/ChromePHPHandler.php

@@ -130,8 +130,10 @@ class ChromePHPHandler extends AbstractProcessingHandler
             $data = base64_encode(utf8_encode($json));
         }
 
+        if (trim($data) !== '') {
             $this->sendHeader(self::HEADER_NAME, $data);
         }
+    }
 
     /**
      * Send header string to the client