wallet: distinguish between empty and absent attributes

src/wallet/wallet2.cpp

@@ -11365,12 +11365,13 @@ void wallet2::set_attribute(const std::string &key, const std::string &value)
   m_attributes[key] = value;
 }
 
-std::string wallet2::get_attribute(const std::string &key) const
+bool wallet2::get_attribute(const std::string &key, std::string &value) const
 {
   std::unordered_map<std::string, std::string>::const_iterator i = m_attributes.find(key);
   if (i == m_attributes.end())
-    return std::string();
-  return i->second;
+    return false;
+  value = i->second;
+  return true;
 }
 
 void wallet2::set_description(const std::string &description)
@@ -11380,7 +11381,10 @@ void wallet2::set_description(const std::string &description)
 
 std::string wallet2::get_description() const
 {
-  return get_attribute(ATTRIBUTE_DESCRIPTION);
+  std::string s;
+  if (get_attribute(ATTRIBUTE_DESCRIPTION, s))
+    return s;
+  return "";
 }
 
 const std::pair<std::map<std::string, std::string>, std::vector<std::string>>& wallet2::get_account_tags()

src/wallet/wallet2.h

@@ -1247,7 +1247,7 @@ private:
      */
     const char* const ATTRIBUTE_DESCRIPTION = "wallet2.description";
     void set_attribute(const std::string &key, const std::string &value);
-    std::string get_attribute(const std::string &key) const;
+    bool get_attribute(const std::string &key, std::string &value) const;
 
     crypto::public_key get_multisig_signer_public_key(const crypto::secret_key &spend_skey) const;
     crypto::public_key get_multisig_signer_public_key() const;

src/wallet/wallet_rpc_server.cpp

@@ -2126,7 +2126,12 @@ namespace tools
       return false;
     }
 
-    res.value = m_wallet->get_attribute(req.key);
+    if (!m_wallet->get_attribute(req.key, res.value))
+    {
+      er.code = WALLET_RPC_ERROR_CODE_ATTRIBUTE_NOT_FOUND;
+      er.message = "Attribute not found.";
+      return false;
+    }
     return true;
   }
   bool wallet_rpc_server::on_get_tx_key(const wallet_rpc::COMMAND_RPC_GET_TX_KEY::request& req, wallet_rpc::COMMAND_RPC_GET_TX_KEY::response& res, epee::json_rpc::error& er, const connection_context *ctx)

src/wallet/wallet_rpc_server_error_codes.h

@@ -75,3 +75,4 @@
 #define WALLET_RPC_ERROR_CODE_SIGN_UNSIGNED          -42
 #define WALLET_RPC_ERROR_CODE_NON_DETERMINISTIC      -43
 #define WALLET_RPC_ERROR_CODE_INVALID_LOG_LEVEL      -44
+#define WALLET_RPC_ERROR_CODE_ATTRIBUTE_NOT_FOUND    -45