fix test error

include/xrpl/protocol/STTx.h

@@ -110,7 +110,7 @@ public:
     getMentionedAccounts() const;
 
     static Blob
-    getSigningData(STTx const& that);
+    getSigningData(STObject const& that);
 
     static Blob
     getSponsorSigningData(STTx const& that);

src/libxrpl/protocol/STTx.cpp

@@ -186,7 +186,7 @@ STTx::getMentionedAccounts() const
 }
 
 Blob
-STTx::getSigningData(STTx const& that)
+STTx::getSigningData(STObject const& that)
 {
     Serializer s;
     s.add32(HashPrefix::txSign);
@@ -507,7 +507,7 @@ multiSignHelper(
     // Make sure the MultiSigners are present.  Otherwise they are not
     // attempting multi-signing and we just have a bad Signers.
     if (!signerObj.isFieldPresent(sfSigners))
-        return Unexpected("Empty Signers.");
+        return Unexpected("Empty SigningPubKey.");
 
     // We don't allow both an sfSigners and an sfTxnSignature.  Both fields
     // being present would indicate that the transaction is signed both ways.

src/test/app/MPToken_test.cpp

@@ -2313,6 +2313,15 @@ class MPToken_test : public beast::unit_test::suite
                 reward = STAmount{sfSignatureReward, USD(10)};
                 minAmount = STAmount{sfMinAccountCreateAmount, mpt};
             }
+            // SponsorshipSet
+            {
+                Json::Value jv;
+                jv[jss::TransactionType] = jss::SponsorshipSet;
+                jv[jss::Account] = alice.human();
+                jv[sfSponsee.fieldName] = carol.human();
+                jv[sfFeeAmount.fieldName] = mpt.getJson(JsonOptions::none);
+                test(jv, sfFeeAmount.fieldName.c_str());
+            }
         }
         BEAST_EXPECT(txWithAmounts.empty());
     }

src/test/jtx/impl/utility.cpp

@@ -47,7 +47,7 @@ void
 sign(Json::Value& jv, Account const& account)
 {
     jv[jss::SigningPubKey] = strHex(account.pk().slice());
-    auto const blob = STTx::getSigningData(STTx{parse(jv)});
+    auto const blob = STTx::getSigningData(parse(jv));
     auto const sig = ripple::sign(account.pk(), account.sk(), makeSlice(blob));
     jv[jss::TxnSignature] = strHex(Slice{sig.data(), sig.size()});
 }