When EnableLogs is true and the log level is below MinimumEventLevel, structured logs are not captured due to the early return on line 98. The test DoAppend_StructuredLoggingWithoutException_LeavesBreadcrumb expects structured logs to be captured in this scenario, and Serilog's implementation captures structured logs independently of event/breadcrumb thresholds. Add CaptureStructuredLog call before the early return, or refactor to call it at the end regardless of the event/breadcrumb path.

Also found at:

• test/Sentry.Log4Net.Tests/SentryAppenderTests.Structured.cs:216

ToSentryLogLevel uses >= comparisons against log4net Level values. log4net's operator >= dereferences the left operand's numeric field without a null check, so a null loggingEvent.Level throws NullReferenceException (the initial level == Level.Off guard is null-safe and falls through). The sibling ToSentryLevel/ToBreadcrumbLevel methods use only ==, which is null-safe and returns null, so those paths handle null gracefully while the structured-log path does not. The thrown NRE is caught by the try/catch around CaptureStructuredLog in Append, so it does not crash the process — but the structured log is silently dropped and an error diagnostic is logged, giving inconsistent behavior versus the event/breadcrumb paths. Add null => null, as the first switch arm to match the other mappers.

Use !string.IsNullOrWhiteSpace(key) instead of key.Length != 0 to match the filtering in GetLoggingEventProperties, which filters whitespace-only keys. Currently, a property key like " " would be included in structured logs but filtered from SentryEvent extras.