@Override
        public String toString() {
            return MoreObjects.toStringHelper(this).omitNullValues()
                              .add("executor", executor)
                              .add("hostname", hostname)
                              .add("address", address)
                              .add("questions", questions)
                              .add("cause", cause)
                              .add("cacheable", cacheable)
                              .add("numAttemptsSoFar", numAttemptsSoFar)
                              .add("originalCreationTimeNanos", originalCreationTimeNanos)
                              .toString();
        }
Closes all the resources allocated and used by this resolver.

<p>Please note that this method does not clear the {@link CacheEntry} because the
{@link #addressResolverCache} is created by {@link RefreshingAddressResolverGroup} and shared across
from all {@link RefreshingAddressResolver}s. {@link CacheEntry} is cleared when
{@link RefreshingAddressResolverGroup#close()} is called.
core/src/main/java/com/linecorp/armeria/client/RefreshingAddressResolver.java