import com.atlassian.jira.component.ComponentAccessor
def customFieldManager = ComponentAccessor.customFieldManager
customFieldManager.customFieldObjects.each {
if (it.name != it.name.trim()) {
log.warn("Modifying field with leading or trailing whitespace: '${it.name}'")
// Update the field - to preview only comment out the following line
customFieldManager.updateCustomField(it.idAsLong, it.name.trim(), it.description, it.customFieldSearcher)
}
}