rpc: document optional fields for getchaintxstats result

Author: theStack

src/rpc/blockchain.cpp

@@ -1668,9 +1668,9 @@ static RPCHelpMan getchaintxstats()
                         {RPCResult::Type::STR_HEX, "window_final_block_hash", "The hash of the final block in the window"},
                         {RPCResult::Type::NUM, "window_final_block_height", "The height of the final block in the window."},
                         {RPCResult::Type::NUM, "window_block_count", "Size of the window in number of blocks"},
-                        {RPCResult::Type::NUM, "window_tx_count", "The number of transactions in the window. Only returned if \"window_block_count\" is > 0"},
-                        {RPCResult::Type::NUM, "window_interval", "The elapsed time in the window in seconds. Only returned if \"window_block_count\" is > 0"},
-                        {RPCResult::Type::NUM, "txrate", "The average rate of transactions per second in the window. Only returned if \"window_interval\" is > 0"},
+                        {RPCResult::Type::NUM, "window_tx_count", /* optional */ true, "The number of transactions in the window. Only returned if \"window_block_count\" is > 0"},
+                        {RPCResult::Type::NUM, "window_interval", /* optional */ true, "The elapsed time in the window in seconds. Only returned if \"window_block_count\" is > 0"},
+                        {RPCResult::Type::NUM, "txrate", /* optional */ true, "The average rate of transactions per second in the window. Only returned if \"window_interval\" is > 0"},
                     }},
                 RPCExamples{
                     HelpExampleCli("getchaintxstats", "")