A `NullPointerException` in the `MetricsRetryListener` when provided `RetryCallback` comes without proper `getLabel()` implementation

[artembilan]

More info in the: spring-projects/spring-integration#9985.
The error looks like this:

java.lang.NullPointerException
	at java.base/java.util.Objects.requireNonNull(Objects.java:208)
	at io.micrometer.core.instrument.ImmutableTag.<init>(ImmutableTag.java:37)
	at io.micrometer.core.instrument.Tag.of(Tag.java:31)
	at io.micrometer.core.instrument.Tags.of(Tags.java:247)
	at org.springframework.retry.support.MetricsRetryListener.close(MetricsRetryListener.java:116)

If we do just this:

SimpleRetryPolicy simpleRetryPolicy = new SimpleRetryPolicy();
RetryContext retryContext = simpleRetryPolicy.open(null);
RetryCallback<Object, Throwable> retryCallback = context -> null;
this.metricsRetryListener.open(retryContext, retryCallback);
this.metricsRetryListener.close(retryContext, retryCallback, null);