Fix for #24

Avoid NullReferenceException if "params" property is null.

Author: tintoy

src/JsonRpc/Reciever.cs

@@ -54,7 +54,7 @@ protected virtual Renor GetRenor(JToken @object)
 
             object requestId = null;
             bool hasRequestId;
-            if (hasRequestId = request.TryGetValue("id", out var id))
+            if (hasRequestId = request.TryGetValue("id", out var id) && requestId != null)
             {
                 var idString = id.Type == JTokenType.String ? (string)id : null;
                 var idLong = id.Type == JTokenType.Integer ? (long?)id : null;
@@ -77,7 +77,7 @@ protected virtual Renor GetRenor(JToken @object)
                 return new InvalidRequest(requestId, "Method not set");
             }
 
-            var hasParams = request.TryGetValue("params", out var @params);
+            var hasParams = request.TryGetValue("params", out var @params) && @params != null;
             if (hasParams && @params.Type != JTokenType.Array && @params.Type != JTokenType.Object)
             {
                 return new InvalidRequest(requestId, "Invalid params");
@@ -95,4 +95,4 @@ protected virtual Renor GetRenor(JToken @object)
             }
         }
     }
-}
+}