Problem with parsing XML file in Groovy script running in Jenkins pipeline - groovy

Question

I need to get some data from an XML document in a groovy script running in the Jenkins pipeline. For this, I use XmlParser(). The problem is that the code I wrote fully works in Groovy on my machine, but as soon as I run it from Jenkins I get an error.
The Groovy code:
#NonCPS
def callTests (String configFile, String pathProjectForAsseration) {
def configFileAsXML = new XmlParser().parseText(configFile)
configFileAsXML.testcases.testcase.each { testline ->
String testFileName = testline['#filename']
String testEndpoint = testline['#endpoint']
String testPassword = testline['#password']
// далее следует логика, не относящаяся к вопросу
}
}
def runTests() {
pathToConfigFileForGroovy = "${PATH_TO_CONFIG_FILE}".replace("\\", "/")
String configFile = readFile(pathToConfigFileForGroovy)
callTests(configFile, pathProjectForAsseration)
}
Example of XML file:
<configuration someAttribute="seomeValue">
<testcases>
<testcase filename="filename" password="password" login="login"/>
<testcase filename="filename" password="password" login="login"
isReal="false"/>
<testcase filename="filename" password="password" login="login"/>
<testcase filename="filename" password="password" login="login"
isReal="false"/>
</testcases>
</configuration>
An error occurs on this line:
configFileAsXML.testcases.testcase.each { testline ->
The error:
org.jenkinsci.plugins.scriptsecurity.sandbox.RejectedAccessException: No such field found: field groovy.util.Node testcases.