{
    "name" : "Italy"
}

<expression-filter expression="regex('^[a-zA-Z]{3,15}$' , 'json:name')" doc:name="Expression"/>

<expression-filter expression="regex('(.*)' , 'json:name')" doc:name="Expression"/>

<set-variable variableName="PayloadBackup" value="#[payload]" doc:name="Variable"/><json:json-to-object-transformer returnClass="java.util.Map" doc:name="JSON to Object"/>
    <expression-transformer expression="#[payload['name'].matches('^[a-zA-Z]{3,15}$')]" doc:name="Expression"/>
    <expression-filter expression="#[payload]" doc:name="Expression"/>
    <set-payload value="#[PayloadBackup]" doc:name="Set Payload"/>

null (java.lang.NullPointerException). Message payload is of type: Boolean