scripted-diff: Replace NullUniValue with UniValue::VNULL

This is required for removing the UniValue copy constructor.

-BEGIN VERIFY SCRIPT-
 sed -i 's/return NullUniValue/return UniValue::VNULL/g' $(git grep -l NullUniValue ':(exclude)src/univalue')
-END VERIFY SCRIPT-

src/rpc/blockchain.cpp

@@ -397,7 +397,7 @@ static RPCHelpMan syncwithvalidationinterfacequeue()
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
 {
     SyncWithValidationInterfaceQueue();
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -1056,11 +1056,11 @@ static RPCHelpMan gettxout()
         LOCK(mempool.cs);
         CCoinsViewMemPool view(coins_view, mempool);
         if (!view.GetCoin(out, coin) || mempool.isSpent(out)) {
-            return NullUniValue;
+            return UniValue::VNULL;
         }
     } else {
         if (!coins_view->GetCoin(out, coin)) {
-            return NullUniValue;
+            return UniValue::VNULL;
         }
     }
 
@@ -1498,7 +1498,7 @@ static RPCHelpMan preciousblock()
         throw JSONRPCError(RPC_DATABASE_ERROR, state.ToString());
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -1539,7 +1539,7 @@ static RPCHelpMan invalidateblock()
         throw JSONRPCError(RPC_DATABASE_ERROR, state.ToString());
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -1579,7 +1579,7 @@ static RPCHelpMan reconsiderblock()
         throw JSONRPCError(RPC_DATABASE_ERROR, state.ToString());
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -2098,7 +2098,7 @@ static RPCHelpMan scantxoutset()
         CoinsViewScanReserver reserver;
         if (reserver.reserve()) {
             // no scan in progress
-            return NullUniValue;
+            return UniValue::VNULL;
         }
         result.pushKV("progress", g_scan_progress.load());
         return result;

src/rpc/mining.cpp

@@ -476,7 +476,7 @@ static RPCHelpMan prioritisetransaction()
 static UniValue BIP22ValidationResult(const BlockValidationState& state)
 {
     if (state.IsValid())
-        return NullUniValue;
+        return UniValue::VNULL;
 
     if (state.IsError())
         throw JSONRPCError(RPC_VERIFY_ERROR, state.ToString());
@@ -1040,7 +1040,7 @@ static RPCHelpMan submitheader()
 
     BlockValidationState state;
     chainman.ProcessNewBlockHeaders({h}, state);
-    if (state.IsValid()) return NullUniValue;
+    if (state.IsValid()) return UniValue::VNULL;
     if (state.IsError()) {
         throw JSONRPCError(RPC_VERIFY_ERROR, state.ToString());
     }

src/rpc/net.cpp

@@ -84,7 +84,7 @@ static RPCHelpMan ping()
 
     // Request that each node send a ping during next message processing pass
     peerman.SendPings();
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -304,7 +304,7 @@ static RPCHelpMan addnode()
     {
         CAddress addr;
         connman.OpenNetworkConnection(addr, false, nullptr, strNode.c_str(), ConnectionType::MANUAL);
-        return NullUniValue;
+        return UniValue::VNULL;
     }
 
     if (strCommand == "add")
@@ -320,7 +320,7 @@ static RPCHelpMan addnode()
         }
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -423,7 +423,7 @@ static RPCHelpMan disconnectnode()
         throw JSONRPCError(RPC_CLIENT_NODE_NOT_CONNECTED, "Node not found in connected nodes");
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -745,7 +745,7 @@ static RPCHelpMan setban()
             throw JSONRPCError(RPC_CLIENT_INVALID_IP_OR_SUBNET, "Error: Unban failed. Requested address/subnet was not previously manually banned.");
         }
     }
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -819,7 +819,7 @@ static RPCHelpMan clearbanned()
 
     node.banman->ClearBanned();
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }

src/rpc/node.cpp

@@ -65,7 +65,7 @@ static RPCHelpMan setmocktime()
         }
     }
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }
@@ -85,7 +85,7 @@ static RPCHelpMan invokedisallowedsyscall()
                 throw std::runtime_error("invokedisallowedsyscall is used for testing only.");
             }
             TestDisallowedSandboxCall();
-            return NullUniValue;
+            return UniValue::VNULL;
         },
     };
 }
@@ -118,7 +118,7 @@ static RPCHelpMan mockscheduler()
     CHECK_NONFATAL(node_context->scheduler);
     node_context->scheduler->MockForward(std::chrono::seconds(delta_seconds));
 
-    return NullUniValue;
+    return UniValue::VNULL;
 },
     };
 }