feat: StoreAddressIntStd() accepts nulls and empty strings (and writes two zero bytes)

Author: justdmitry

TonLibDotNet.Tests/Cells/CellBuilderTests.cs

@@ -64,6 +64,18 @@ public void WritesAddressesOk()
             slice.EndRead();
         }
 
+        [Fact]
+        public void WritesEmptyAddressesOk()
+        {
+            var cell = new CellBuilder()
+                .StoreAddressIntStd(string.Empty)
+                .Build();
+
+            var slice = cell.BeginRead();
+            Assert.Null(slice.TryLoadAddressIntStd());
+            slice.EndRead();
+        }
+
         [Fact]
         public void WritesCoinsOk()
         {

TonLibDotNet/Extensions/TonClientCellsAddressExtensions.cs

@@ -49,8 +49,15 @@ public static string LoadAddressIntStd(this Slice slice, bool bounceable = true,
             return LoadAddressIntStd(slice, bounceable, testnetOnly, urlSafe);
         }
 
-        public static CellBuilder StoreAddressIntStd(this CellBuilder builder, string address)
+        public static CellBuilder StoreAddressIntStd(this CellBuilder builder, string? address)
         {
+            if (string.IsNullOrEmpty(address))
+            {
+                builder.StoreBit(false);
+                builder.StoreBit(false);
+                return builder;
+            }
+
             if (!AddressValidator.TryParseAddress(address, out var workchainId, out var accountId, out _, out _, out _))
             {
                 throw new ArgumentException("Not a valid address", nameof(address));