Bulk Update the Value of a Custom Field on Jira Cloud Issues

// Specify all the required parameters
def projectKey = 'TEST'
def customFieldName = 'Story Points'
def newCustomFieldValue = 100

// Extract issue key using JQL Query
Issues.search("project = $projectKey and '${customFieldName}' is not EMPTY").each { issue ->
    issue.update  {
        setCustomFieldValue(customFieldName, newCustomFieldValue)
    }
}