Custom Primary Key Field in Recipients has ! icon

Hi Team,

We recently added a custom primary key to the recipents table and used the below format,

<element desc="Recipient table (profiles" img="nms:recipient.png" label="Recipients"
labelSingular="Recipient" name="recipient">
<dbindex name="customerIdIndex" unique="true">
<keyfield xpath="@customerId"/>
</dbindex>
<attribute label="Customer Id" length="100" name="customerId" type="string"/>

.....

The field is functioning as expected(does not allow duploicates), but the field icon has an ! in it?

What does that mean? are we missing something?

Just want to be sure!!

Thanks,

Shine v.v