The CaptureStructuredLog call is placed after the early return at line 97-98, so structured logs are never captured for events below MinimumEventLevel. The test DoAppend_StructuredLoggingWithoutException_LeavesBreadcrumb expects structured logs to be captured even for breadcrumb-only events, but this code path returns before reaching CaptureStructuredLog.

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.