in slf4j-to-log4j-api/src/main/java/org/apache/logging/slf4j/Log4jMDCAdapter.java [98:106]
public Deque<String> getCopyOfDequeByKey(final String key) {
if (key == null) {
final ContextStack stack = ThreadContext.getImmutableStack();
final Deque<String> copy = new ArrayDeque<>(stack.size());
stack.forEach(copy::push);
return copy;
}
return mapOfStacks.getCopyOfDequeByKey(key);
}