code review fix

Change-Id: Ie616543094aaa31d596980ba7a3cef05de4351fc
diff --git a/src/challenge/challenge-email.cpp b/src/challenge/challenge-email.cpp
index ba0a0e8..af0303e 100644
--- a/src/challenge/challenge-email.cpp
+++ b/src/challenge/challenge-email.cpp
@@ -124,7 +124,7 @@
 
 Block
 ChallengeEmail::genChallengeRequestTLV(Status status, const std::string& challengeStatus,
-                                       std::multimap<std::string, std::string>&& params)
+                                       const std::multimap<std::string, std::string>& params)
 {
   Block request(tlv::EncryptedPayload);
   if (status == Status::BEFORE_CHALLENGE) {