After switching to Sleuth 3.0.2 TracerContext is always null

Question

I have upgraded Sleuth to version 3.0.2 and started getting NPEs. I know that there were breaking changes, and there is a migration guide, but for the life of me I cannot say how to resolve this issue.

[INFO] +- org.springframework.cloud:spring-cloud-starter-sleuth:jar:3.0.2:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter-aop:jar:2.4.5:compile
[INFO] |  |  \- org.aspectj:aspectjweaver:jar:1.9.6:compile
[INFO] |  +- org.springframework.cloud:spring-cloud-sleuth-autoconfigure:jar:3.0.2:compile
[INFO] |  |  +- org.springframework.cloud:spring-cloud-sleuth-instrumentation:jar:3.0.2:compile
[INFO] |  |  |  \- org.springframework.cloud:spring-cloud-sleuth-api:jar:3.0.2:compile
[INFO] |  |  \- org.aspectj:aspectjrt:jar:1.9.6:compile
[INFO] |  \- org.springframework.cloud:spring-cloud-sleuth-brave:jar:3.0.2:compile
[INFO] |     +- io.zipkin.brave:brave:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-context-slf4j:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-messaging:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-rpc:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-spring-rabbit:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-kafka-clients:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-kafka-streams:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-httpclient:jar:5.13.2:compile
[INFO] |     |  \- io.zipkin.brave:brave-instrumentation-http:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-httpasyncclient:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-jms:jar:5.13.2:compile
[INFO] |     +- io.zipkin.brave:brave-instrumentation-mongodb:jar:5.13.2:compile
[INFO] |     +- io.zipkin.aws:brave-propagation-aws:jar:0.21.3:compile
[INFO] |     \- io.zipkin.reporter2:zipkin-reporter-metrics-micrometer:jar:2.16.1:compile
[INFO] |        \- io.zipkin.reporter2:zipkin-reporter:jar:2.16.1:compile
[INFO] |           \- io.zipkin.zipkin2:zipkin:jar:2.23.0:compile

The field that is being injected.

@Autowired
protected Tracer tracer;

The line that is throwing NPE:

tracer.currentSpan().context().traceId();

The currentSpan() method, where ThreadContext is null.

@Nullable
public Span currentSpan() {
    TraceContext context = this.currentTraceContext.get();
    return context == null ? null : new LazySpan(this, context);
}

Also this line is producing null: String traceId = MDC.get("X-B3-TraceId");

MDC.getCopyOfContextMap(); returns an empty map.

Here is the code of the method for the completeness of the picture:

@GetMapping(path = "/user", produces = APPLICATION_JSON_VALUE)
@RequiresPermissions(IAM_USER_GET_PERMISSION)
public Object getMyself() {
    UserContext userContext = (UserContext) SecurityUtils.getSubject().getPrincipal();
    String traceId = MDC.get("X-B3-TraceId");
    System.out.println(traceId);
    System.out.println(MDC.getCopyOfContextMap());
    OperationContext operationContext = OperationContext.newInstance(userContext, tracer.currentSpan().context().traceId());
    UserBO user = identityManager.getMyself(operationContext);
    return ResponseEntity.status(HttpStatus.OK).body(new UserEnvelopeDTO(iamDTOMapper.mapScoped(user, user.getActiveOrganizationId())));
}

As you can see this is an HTTP thread, that doesn't get MDC properly populated.

Also, I have this bean configured:

@Bean
public CurrentTraceContext.ScopeDecorator legacyMDCKeys() {
    return MDCScopeDecorator.newBuilder()
            .clear()
            .add(CorrelationScopeConfig.SingleCorrelationField.newBuilder(BaggageFields.TRACE_ID)
                    .name("X-B3-TraceId").build())
            .add(CorrelationScopeConfig.SingleCorrelationField.newBuilder(BaggageFields.PARENT_ID)
                    .name("X-B3-ParentSpanId").build())
            .add(CorrelationScopeConfig.SingleCorrelationField.newBuilder(BaggageFields.SPAN_ID)
                    .name("X-B3-SpanId").build())
            .add(CorrelationScopeConfig.SingleCorrelationField.newBuilder(BaggageFields.SAMPLED)
                    .name("X-Span-Export").build())
            .build();
}