rpc: Use Join helper in rpc/util

src/rpc/util.cpp

@@ -4,11 +4,12 @@
 
 #include <key_io.h>
 #include <outputtype.h>
-#include <script/signingprovider.h>
 #include <rpc/util.h>
 #include <script/descriptor.h>
+#include <script/signingprovider.h>
 #include <tinyformat.h>
 #include <util/strencodings.h>
+#include <util/string.h>
 
 #include <tuple>
 
@@ -645,11 +646,7 @@ std::string RPCArg::ToString(const bool oneline) const
     }
     case Type::OBJ:
     case Type::OBJ_USER_KEYS: {
-        std::string res;
-        for (size_t i = 0; i < m_inner.size();) {
-            res += m_inner[i].ToStringObj(oneline);
-            if (++i < m_inner.size()) res += ",";
-        }
+        const std::string res = Join(m_inner, ",", [&](const RPCArg& i) { return i.ToStringObj(oneline); });
         if (m_type == Type::OBJ) {
             return "{" + res + "}";
         } else {