fixDatetimeNanos() doesn't manage date time without nano precision

[fredmef]

Steps to reproduce:
List the minimal actions needed to reproduce the behavior.

1. Create a task using postTasks() through TasksService
2. The date time returned by postTasksWithHttpInfo() is in second precision

Expected behavior:
Describe what you expected to happen.

When the date time returned by postTasksWithHttpInfo() is in second, fixDatetimeNanos() doesn't crash.

fixDatetimeNanos() shall check the size returned by explode() before accessing the array elements.

static function fixDatetimeNanos(string $date) : string {
    $dateParts = explode(".", $date);
    $nanosZ = $dateParts[1];
    $posZ = strpos($nanosZ, 'Z');
    if (strlen($nanosZ) > 9) {
        $converted = $dateParts[0] . "." . substr($nanosZ, 0, 8);
        if ($posZ > 0) {
            $converted .= "Z";
        }
        return $converted;
    } else {
        return $date;
    }
}

Actual behavior:
Describe What actually happened.

Here is the PHP log for postTasks():

Notice: Undefined offset: 1 in InfluxDB2\ObjectSerializer::fixDatetimeNanos() (line 340 of /var/www/html/vendor/influxdata/influxdb-client-php/src/InfluxDB2/ObjectSerializer.php).
InfluxDB2\ObjectSerializer::fixDatetimeNanos('2021-09-27T07:31:07Z') (Line: 272)
InfluxDB2\ObjectSerializer::deserialize('2021-09-27T07:31:07Z', '\DateTime', NULL) (Line: 323)
InfluxDB2\ObjectSerializer::deserialize(Object, '\InfluxDB2\Model\Task', Array) (Line: 4607)
InfluxDB2\Service\TasksService->postTasksWithHttpInfo(Object, NULL) (Line: 4549)
InfluxDB2\Service\TasksService->postTasks(Object) (Line: 99)

Specifications:

• Client Version: 2.2.0
• InfluxDB Version: 2.0.8
• Platform: Docker (Drupal 9)