merge bitcoin#24855: Fix setwalletflag disabling of flags

Author: kwvg

src/wallet/rpc/wallet.cpp

@@ -560,7 +560,7 @@ static RPCHelpMan setwalletflag()
             {
                 {RPCResult::Type::STR, "flag_name", "The name of the flag that was modified"},
                 {RPCResult::Type::BOOL, "flag_state", "The new state of the flag"},
-                {RPCResult::Type::STR, "warnings", "Any warnings associated with the change"},
+                {RPCResult::Type::STR, "warnings", /*optional=*/true, "Any warnings associated with the change"},
             }
         },
         RPCExamples{

test/functional/wallet_avoidreuse.py

@@ -115,6 +115,17 @@ def test_persistence(self):
         assert_raises_rpc_error(-8, "Wallet flag is already set to false", self.nodes[0].setwalletflag, 'avoid_reuse', False)
         assert_raises_rpc_error(-8, "Wallet flag is already set to true", self.nodes[1].setwalletflag, 'avoid_reuse', True)
 
+        # Create a wallet with avoid reuse, and test that disabling it afterwards persists
+        self.nodes[1].createwallet(wallet_name="avoid_reuse_persist", avoid_reuse=True)
+        w = self.nodes[1].get_wallet_rpc("avoid_reuse_persist")
+        assert_equal(w.getwalletinfo()["avoid_reuse"], True)
+        w.setwalletflag("avoid_reuse", False)
+        assert_equal(w.getwalletinfo()["avoid_reuse"], False)
+        w.unloadwallet()
+        self.nodes[1].loadwallet("avoid_reuse_persist")
+        assert_equal(w.getwalletinfo()["avoid_reuse"], False)
+        w.unloadwallet()
+
     def test_immutable(self):
         '''Test immutable wallet flags'''
         self.log.info("Test immutable wallet flags")