[ML][Rules] Fixes deletion in Check interval input for anomaly detect…

…ion rule (elastic#193420)

## Summary

It was trying to parse `null` values.
After:

![image](https://github.com/user-attachments/assets/82d24663-a895-4ad4-bc01-fb76b883bc66)

Fixes [elastic#190732](elastic#190732)

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
(cherry picked from commit 65b7bf9)

x-pack/plugins/ml/public/alerting/anomaly_detection_rule/config_validator.tsx

@@ -32,13 +32,15 @@ export const ConfigValidator: FC<ConfigValidatorProps> = React.memo(
   ({ jobConfigs = [], alertInterval, alertParams, alertNotifyWhen, maxNumberOfBuckets }) => {
     if (jobConfigs.length === 0) return null;
 
-    const alertIntervalInSeconds = parseInterval(alertInterval)!.asSeconds();
+    const alertIntervalInSeconds = parseInterval(alertInterval)?.asSeconds();
 
     const lookbackIntervalInSeconds =
       !!alertParams.lookbackInterval && parseInterval(alertParams.lookbackInterval)?.asSeconds();
 
     const isAlertIntervalTooHigh =
-      lookbackIntervalInSeconds && lookbackIntervalInSeconds < alertIntervalInSeconds;
+      lookbackIntervalInSeconds &&
+      alertIntervalInSeconds &&
+      lookbackIntervalInSeconds < alertIntervalInSeconds;
 
     const jobWithoutStartedDatafeed = jobConfigs
       .filter((job) => job.datafeed_config.state !== DATAFEED_STATE.STARTED)
@@ -49,6 +51,7 @@ export const ConfigValidator: FC<ConfigValidatorProps> = React.memo(
     const notifyWhenWarning =
       alertNotifyWhen === 'onActiveAlert' &&
       lookbackIntervalInSeconds &&
+      alertIntervalInSeconds &&
       alertIntervalInSeconds < lookbackIntervalInSeconds;
 
     const bucketSpanDuration = parseInterval(jobConfigs[0].analysis_config.bucket_span!);