Until-Successful failureExpression condition not working - mule

Question

I created a simple flow which creates a list of names transforms it. The transformer throws an IllegalArgumentException to break the flow. Unfortunately, the failureExpression does not work even though an exception is thrown. It doesn't match any exceptions. I have included the flow and the transformer.
Here is my configuration:
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:scripting="http://www.mulesoft.org/schema/mule/scripting"
xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns="http://www.mulesoft.org/schema/mule/core"
xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans" xmlns:vm="http://www.mulesoft.org/schema/mule/vm"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.mulesoft.org/schema/mule/scripting
http://www.mulesoft.org/schema/mule/scripting/current/mule-scripting.xsd
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core
http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/vm
http://www.mulesoft.org/schema/mule/vm/current/mule-vm.xsd
http://www.mulesoft.org/schema/mule/http
http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd">
<spring:beans>
<spring:bean name="transf" class="com.until.sucessful.tests.StringAppenderTransformer" />
<spring:bean id="objectStore" class="org.mule.util.store.SimpleMemoryObjectStore" />
</spring:beans>
<http:listener-config name="HTTP_Listener_Configuration" host="0.0.0.0" port="8081" doc:name="HTTP Listener Configuration" />
<flow name="untilsuccessfultestsFlow">
<http:listener config-ref="HTTP_Listener_Configuration" path="/mytest" doc:name="HTTP" />
<splitter expression="#[xpath3('//Names')]" doc:name="Splitter" />
<until-successful maxRetries="5" millisBetweenRetries="5000" doc:name="Until Successful" objectStore-ref="objectStore" failureExpression="#[exception is java.lang.IllegalArgumentException)]">
<vm:outbound-endpoint path="process-vm" exchange-pattern="request-response" />
</until-successful>
<logger level="INFO" message="After the scoped processor :: #[payload]" doc:name="Logger" />
</flow>
<flow name="processorFlow">
<vm:inbound-endpoint path="process-vm" exchange-pattern="request-response" />
<logger level="INFO" message="Before component #[payload]" doc:name="Logger" />
<transformer ref="transf" />
</flow>
</mule>
Here is my Transformer
public class StringAppenderTransformer extends AbstractTransformer {
#Override
protected Object doTransform(Object src, String enc) throws TransformerException {
String payload = (String) src;
List<String> results = new ArrayList<>();
System.out.println("Upon entry in transformer payload is :: " + payload);
System.out.println("About to return from transformer payload is :: " + payload.split("\\s+"));
int i = 1;
for (String args : payload.split("\\s+")) {
System.out.println("" + i + " " + args);
i++;
if (args != null && args.trim().equals("")) {
results.add(args);
} else {
throw new IllegalArgumentException("Break the Flow!!!!!!");
}
}
return results;
}
}

Answer 1

According to documentation :
https://docs.mulesoft.com/mule-user-guide/v/3.5/until-successful-scope
failureExpression
Specifies an expression that, when it evaluated to true, determines
that the processing of one route was a failure. If no expression is
provided, only an exception will be treated as a processing failure.
So 2 options, remove that expression or be sure that the MEL return true. #[exception.causeMatches("java.lang.IllegalArgumentException")]