required validator
Description
RequiredFieldValidator checks if the specified field is not null.
Parameters
fieldName- field name if plain-validator syntax is used, not needed if field-validator syntax is used.
Examples
<validators>
<!-- Plain Validator Syntax -->
<validator type="required">
<param name="fieldName">username</param>
<message>username must not be null</message>
</validator>
<!-- Field Validator Syntax -->
<field name="username">
<field-validator type="required">
<message>username must not be null</message>
</field-validator>
</field>
</validators>