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# 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>