# Elastic APM - Object reference not set to an instance of an object

**URL:** <https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089>\
**Category:** APM\
**Tags:** dotnet\
**Created:** [January 4, 2021, 12:03pm UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089 "2021-01-04T12:03:19Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![LandgrafJ](https://avatars.discourse-cdn.com/v4/letter/l/9d8465/32.png) [@LandgrafJ](https://discuss.elastic.co/u/LandgrafJ)\
**Post date:** [January 4, 2021, 12:03pm UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089/1 "2021-01-04T12:03:20Z")

</div>

**Kibana version** : N/A

**Elasticsearch version** : N/A

**APM Server version** : N/A

**APM Agent language and version** : C# .NET 4.6.1, agent v1.7.1

**Browser version** : N/A

**Original install method (e.g. download page, yum, deb, from source, etc.) and version**: nuget

**Fresh install or upgraded from other version?** fresh

**Is there anything special in your setup?** n/a

**Description of the problem including expected versus actual behavior. Please include screenshots (if relevant)**:

Hi, I am trying to have a semi-dynamic agent on a .net stack.  
It worked on previous version, but now I get an

```
Object reference not set to an instance of an object.
   at Elastic.Apm.Helpers.WildcardMatcher.AnyMatch(IReadOnlyCollection`1 matchers, String firstPart, String secondPart)
   at Elastic.Apm.Metrics.MetricsCollector..ctor(IApmLogger logger, IPayloadSender payloadSender, IConfigSnapshotProvider configSnapshotProvider)
   at Elastic.Apm.AgentComponents..ctor(IApmLogger logger, IConfigurationReader configurationReader, IPayloadSender payloadSender, IMetricsCollector metricsCollector, ICurrentExecutionSegmentsContainer currentExecutionSegmentsContainer, ICentralConfigFetcher centralConfigFetcher, IApmServerInfo apmServerInfo)

```

My code is as follows:

```auto
class ConfigReader : IConfigurationReader
	{
		public string CaptureBody { get; set; } = "all";
		public List<string> CaptureBodyContentTypes { get; set; } = null;
		public bool CaptureHeaders { get; set; } = true;
		public bool CentralConfig { get; set; } = true;
		public string Environment { get; set; } = "production";
		public TimeSpan FlushInterval { get; set; } = TimeSpan.FromSeconds(10);
		public IReadOnlyDictionary<string, string> GlobalLabels => new Dictionary<string, string>();
		public Elastic.Apm.Logging.LogLevel LogLevel { get; set; } = Elastic.Apm.Logging.LogLevel.Debug;
		public int MaxBatchEventCount { get; set; } = 1000;
		public int MaxQueueEventCount { get; set; } = 1000;
		public double MetricsIntervalInMilliseconds { get; set; }
		public IReadOnlyList<WildcardMatcher> SanitizeFieldNames { get; set; }
		public string SecretToken { get; set; }
		public IReadOnlyList<Uri> ServerUrls { get; set; }
		public string ServiceName{ get; set; }
		public string ServiceVersion { get; set; }
		public double SpanFramesMinDurationInMilliseconds { get; set; } = 100;
		public int StackTraceLimit { get; set; } = 100;
		public int TransactionMaxSpans { get; set; } = 500;
		public double TransactionSampleRate { get; set; } = 1.0;
        public string ApiKey { get; set; }
		public IReadOnlyCollection<string> ApplicationNamespaces { get; set; }
		public string CloudProvider { get; set; }
		public IReadOnlyList<WildcardMatcher> DisableMetrics { get; set; }
		public bool Enabled { get; set; } = true;
        public IReadOnlyCollection<string> ExcludedNamespaces { get; set; }
		public string HostName { get; set; }
		public bool Recording { get; set; } = true;
		public string ServiceNodeName { get; set; }
		public IReadOnlyList<WildcardMatcher> TransactionIgnoreUrls { get; set; }
		public bool UseElasticTraceparentHeader { get; set; }
		public bool VerifyServerCert { get; set; }
		public ConfigReader(string ssServerUrl, string ssSecretToken, string ssServiceName, string ssServiceVersion, int ssMetricsIntervalMs)
		{
			ServerUrls = new List<Uri>	{new Uri(ssServerUrl)};
			ServiceName = ssServiceName;
			ServiceVersion = ssServiceVersion;
			SecretToken = ssSecretToken;
			MetricsIntervalInMilliseconds = ssMetricsIntervalMs;
		}
	}

someInitAction(...) {
if (!Agent.IsConfigured)
    			{
    				var configReader = new ConfigReader(ssServerUrl, ssSecretToken, ssServiceName, ssServiceVersion, ssMetricsIntervalMs)
    				{
    					Environment = AppInfo.GetAppInfo().EnvironmentName
    				};
    				Agent.Setup(new AgentComponents(null, configReader, null));
    				Agent.Subscribe(new HttpDiagnosticsSubscriber());
    			}
    			ssSuccess = Agent.IsConfigured;
}

```

---

<div class="post-metadata">

**Author:** ![GregKalapos](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/gregkalapos/32/37205_2.png) [@GregKalapos](https://discuss.elastic.co/u/GregKalapos)\
**Post date:** [January 4, 2021, 12:59pm UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089/2 "2021-01-04T12:59:42Z")

</div>

Hi @LandgrafJ,

My first candidate is the `IReadOnlyList<WildcardMatcher> DisableMetrics` in your `ConfigReader`.

It seems our `Elastic.Apm.Helpers.WildcardMatcher` can't handle when it gets a `null` in the `IReadOnlyList<WildcardMatcher>` parameter and that comes from the `DisableMetrics` property of `IConfigurationReader`.

Could you try to return an empty list for the `DisableMetrics` property instead of `null` as an immediate workaround?

Having said that - I'd say the agent should be able to deal with an `IConfigurationReader` which returns `null` for `DisableMetrics`. I'll look into that and try to see if we can fix it in a future version.

---

<div class="post-metadata">

**Author:** ![LandgrafJ](https://avatars.discourse-cdn.com/v4/letter/l/9d8465/32.png) [@LandgrafJ](https://discuss.elastic.co/u/LandgrafJ)\
**Post date:** [January 4, 2021, 1:21pm UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089/3 "2021-01-04T13:21:13Z")

</div>

Hi,

Yes, that workaround did the trick.  
But indeed it's a bit unexpected.

---

<div class="post-metadata">

**Author:** ![GregKalapos](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/gregkalapos/32/37205_2.png) [@GregKalapos](https://discuss.elastic.co/u/GregKalapos)\
**Post date:** [January 4, 2021, 3:05pm UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089/4 "2021-01-04T15:05:53Z")

</div>

I [opened a PR](https://github.com/elastic/apm-agent-dotnet/pull/1109) to make sure this doesn't happen in the future.

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [January 25, 2021, 11:05am UTC](https://discuss.elastic.co/t/elastic-apm-object-reference-not-set-to-an-instance-of-an-object/260089/5 "2021-01-25T11:05:57Z")

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