Alert message error

Hi All,

We have scheduled Alerts in PI7.4 singlestack.

But we are getting an unwanted text in mail subject and body as below.

Subject: #Adv#:[null]1 message failed for "DEFAULT_ALERTRULE"

Body: [null]1 message failed for "DEFAULT_ALERTRULE"

I am not sure why this null is coming.

Please suggest.

Thanks & Regards,

Nida