Fix `DNSProtoBufMessage::toDebugString()` without protobuf support

Fixes #4240.

diff --git a/pdns/protobuf.cc b/pdns/protobuf.cc
index 248fd608defc8ac443bd9c782d675e89bc9fed8d..d04fa2540b1a702a88d2fbd577e822034080d540 100644 (file)
--- a/pdns/protobuf.cc
+++ b/pdns/protobuf.cc
@@ -151,6 +151,8 @@ std::string DNSProtoBufMessage::toDebugString() const
 {
 #ifdef HAVE_PROTOBUF
   return d_message.DebugString();
+#else
+  return std::string();
 #endif /* HAVE_PROTOBUF */
 }