FIX: Neo.Network.RPC.Utility.RuleExpressionFromJson

[Devel484]

Describe the bug
Fetching a block on testnet causes a crash in RPC Client.

Neo.Network.RPC.Models.RpcTransaction
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at Neo.Network.RPC.Utility.RuleExpressionFromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.Utility.RuleFromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.Utility.<>c__DisplayClass11_0.<SignerFromJson>b__0(JToken p)
   at System.Linq.Enumerable.SelectIListIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Neo.Network.RPC.Utility.SignerFromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.Utility.<>c__DisplayClass9_0.<TransactionFromJson>b__0(JToken p)
   at System.Linq.Enumerable.SelectIListIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Neo.Network.RPC.Utility.TransactionFromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.Utility.<>c__DisplayClass6_0.<BlockFromJson>b__0(JToken p)
   at System.Linq.Enumerable.SelectIListIterator`2.ToArray()
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Neo.Network.RPC.Utility.BlockFromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.Models.RpcBlock.FromJson(JObject json, ProtocolSettings protocolSettings)
   at Neo.Network.RPC.RpcClient.GetBlockAsync(String hashOrIndex)

To Reproduce
Steps to reproduce the behavior:

1. Use N3 RPC 3.5.0
2. Use any N3 Node(e.g. http://seed1t5.neo.org:20332)
3. Query block 1048534

var block = await rpc.GetBlockAsync("1048534");