The Grails Framework 4.0.11

(Quick Reference) ## nullable ### Purpose Allows a property to be set to `null`. By default Grails does not allow `null` values for properties. ### Examples
    age nullable: true
### Description Set to `true` if the property allows `null` values. This constraint influences schema generation. Error Code: `className.propertyName.nullable`
| Web requests resulting from form submissions will have blank strings, not `null`, for input fields that have no value. Keep this in mind when doing mass property binding to properties that are not nullable. The default behavior is such that a blank string will not validate for `nullable: false` since the data binder will convert blank strings to null. This includes empty strings and blank strings. A blank string is any string such that the `trim()` method returns an empty string. To turn off the conversion of empty strings to null set the `grails.databinding.convertEmptyStringsToNull` property to `false` in `application.groovy`. See the data binding section for more details on data binding.
grails-app/conf/application.groovy
    // the default value for this property is true
    grails.databinding.convertEmptyStringsToNull = false

    // ...
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