source/core-developers/required-validator.md

---
layout: default
title: required validator
parent:
    title: Validation
    url: validation.html
---

# required validator
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* Will be replaced with the ToC, excluding a header
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## 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

```xml
<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>
```