Hi just recently installed the SteamChecks plugin, everything is working fine but currently getting this error every 3-5 minutes, 
Thanks!

Web request callback raised an exception (ArgumentNullException: Value cannot be null
Parameter name: value)
at Newtonsoft.Json.Linq.JToken.EnsureValue (Newtonsoft.Json.Linq.JToken value) [0x00003] in <45c13f2b01574d8b82248736e42013a4>:0
at Newtonsoft.Json.Linq.JToken.op_Explicit (Newtonsoft.Json.Linq.JToken value) [0x00000] in <45c13f2b01574d8b82248736e42013a4>:0
at Oxide.Plugins.SteamChecks+<GetSteamLevel>c__AnonStorey6.<>m__0 (System.Int32 httpCode, Newtonsoft.Json.Linq.JObject jsonResponse) [0x00027] in <bf7de1419ac34c4d94a2a100a58d8bd9>:0
at Oxide.Plugins.SteamChecks+<SteamWebRequest>c__AnonStorey5.<>m__0 (System.Int32 httpCode, System.String response) [0x00018] in <bf7de1419ac34c4d94a2a100a58d8bd9>:0
at Oxide.Core.Libraries.WebRequests+WebRequest.<OnComplete>b__42_0 () [0x00034] in <ec05e0208c9149bba43236ca58fea105>:0

Yep, sometimes the SteamAPI just returns an empty response. Thats kind of random and seems to happen to some servers more often, for some less (and not always).

Not really fixable, but I have already a local fix for the stacktrace, which will supress it. I will push it some time at the end of the week.

When the SteamAPI returns something unexpected like this, the user will be let through.