docs: explain why EventProvider lock is nullable

Signed-off-by: marcozabel <marco.zabel@dynatrace.com>

Author: marcozabel

src/main/java/dev/openfeature/sdk/EventProvider.java

@@ -99,6 +99,9 @@ public Awaitable emit(final ProviderEvent event, final ProviderEventDetails deta
         // These calls need to be executed on a different thread to prevent deadlocks when the provider initialization
         // relies on a ready event to be emitted
         emitterExecutor.submit(() -> {
+            // The lock is null when the provider has not been attached to an API instance yet.
+            // In that case, we skip locking; the listener/emitter are already captured as local
+            // variables above, so there is no race with a concurrent attach/detach.
             try (var ignored = localLock != null ? localLock.readLockAutoCloseable() : null) {
                 if (localEventProviderListener != null) {
                     localEventProviderListener.onEmit(event, details);