Avoid crash in Transaction.ToString if value or scriptpubkey is null

Author: NicolasDorier

NBitcoin.Tests/TaprootAddressTests.cs

@@ -119,6 +119,7 @@ public void CanSignUsingTaproot()
 		}
 
 		[Fact]
+		[Trait("UnitTest", "UnitTest")]
 		public void CanSignUsingTapscriptAndKeySpend()
 		{
 			var ctx = Context.Instance;

NBitcoin.Tests/transaction_tests.cs

@@ -19,6 +19,7 @@
 using Xunit.Abstractions;
 using Encoders = NBitcoin.DataEncoders.Encoders;
 using static NBitcoin.Tests.Helpers.PrimitiveUtils;
+using NBitcoin.Altcoins;
 
 namespace NBitcoin.Tests
 {
@@ -2624,6 +2625,7 @@ public void CanParseElementsStuff()
 			tx = (ElementsTransaction)Transaction.Parse(txStr, Altcoins.Liquid.Instance.Mainnet);
 			var id = ((ElementsTxIn)tx.Inputs[0]).GetIssuedAssetId();
 			Assert.Equal("140ad0392c3aa83f8fa31722ca2ecfcf582499a4dc9e63a8e44c9b405cb148fe", id.ToString());
+			tx.ToString();
 		}
 
 		[Fact]
@@ -3136,6 +3138,7 @@ public void CanParseTransaction()
 		}
 
 		[Fact]
+		[Trait("UnitTest", "UnitTest")]
 		public void DoNotCrashOnRegtest()
 		{
 			Assert.NotNull(Network.GetNetwork("regtest"));

NBitcoin/RPC/BlockExplorerFormatter.cs

@@ -79,8 +79,8 @@ static internal void WriteTransaction(JsonTextWriter writer, Transaction tx)
 			foreach (var txout in tx.Outputs)
 			{
 				writer.WriteStartObject();
-				WritePropertyValue(writer, "value", txout.Value.ToString(false, false));
-				WritePropertyValue(writer, "scriptPubKey", txout.ScriptPubKey.ToString());
+				WritePropertyValue(writer, "value", txout.Value?.ToString(false, false));
+				WritePropertyValue(writer, "scriptPubKey", txout.ScriptPubKey?.ToString());
 				writer.WriteEndObject();
 			}
 			writer.WriteEndArray();