rpc: Implement RPCHelpMan::ArgValue<> for UniValue

Author: MarcoFalke

src/rpc/util.cpp

@@ -678,11 +678,13 @@ static void CheckRequiredOrDefault(const RPCArg& param)
     void force_semicolon(ret_type)
 
 // Optional arg (without default). Can also be called on required args, if needed.
+TMPL_INST(nullptr, const UniValue*, maybe_arg;);
 TMPL_INST(nullptr, std::optional<double>, maybe_arg ? std::optional{maybe_arg->get_real()} : std::nullopt;);
 TMPL_INST(nullptr, std::optional<bool>, maybe_arg ? std::optional{maybe_arg->get_bool()} : std::nullopt;);
 TMPL_INST(nullptr, const std::string*, maybe_arg ? &maybe_arg->get_str() : nullptr;);
 
 // Required arg or optional arg with default value.
+TMPL_INST(CheckRequiredOrDefault, const UniValue&, *CHECK_NONFATAL(maybe_arg););
 TMPL_INST(CheckRequiredOrDefault, bool, CHECK_NONFATAL(maybe_arg)->get_bool(););
 TMPL_INST(CheckRequiredOrDefault, int, CHECK_NONFATAL(maybe_arg)->getInt<int>(););
 TMPL_INST(CheckRequiredOrDefault, uint64_t, CHECK_NONFATAL(maybe_arg)->getInt<uint64_t>(););