fix: Null reference exception in Asp.NET Core 6+ browser monitoring injection. (#3102)

Author: tippmar-nr

src/Agent/NewRelic/Agent/Core/Agent.cs

@@ -324,7 +324,7 @@ public async Task TryInjectBrowserScriptAsync(string contentType, string request
 
  if (rumBytes == null)
  {
- transaction.LogFinest("Skipping RUM Injection: No script was available.");
+ transaction?.LogFinest("Skipping RUM Injection: No script was available.");
  await baseStream.WriteAsync(buffer, 0, buffer.Length);
  }
  else

src/Agent/NewRelic/Agent/Extensions/Providers/Wrapper/AspNetCore6Plus/BrowserInjectionMiddleware.cs

@@ -21,13 +21,16 @@ public BrowserInjectionMiddleware(RequestDelegate next, IAgent agent)
 
  public Task Invoke(HttpContext context)
  {
- if (!BrowserInjectingStreamWrapper.Disabled)
+ // don't invoke the middleware if browser injection is disabled or if we don't have a valid transaction
+ if (BrowserInjectingStreamWrapper.Disabled || !_agent.CurrentTransaction.IsValid)
  {
- // wrap the response body in our stream wrapper which will inject the RUM script if appropriate
- using var injectedResponse = new BrowserInjectingStreamWrapper(_agent, context.Response.Body, context);
- context.Features.Set<IHttpResponseBodyFeature>(new StreamResponseBodyFeature(injectedResponse));
+ return _next(context);
  }
 
+ // wrap the response body in our stream wrapper which will inject the RUM script if appropriate
+ using var injectedResponse = new BrowserInjectingStreamWrapper(_agent, context.Response.Body, context);
+ context.Features.Set<IHttpResponseBodyFeature>(new StreamResponseBodyFeature(injectedResponse));
+
  return _next(context);
  }
  }