Multiple-statement conditions fail to evaluate in MVELRoutingRule

[JeongDaeKim]

Conditions or actions containing multiple statements fail to evaluate, even though MVEL supports multiple statements.

For example:

a = new String("asdf"); "asdf".equals(a)

or including functions

def isNullOrEmpty(s) { s == null || s.isEmpty() }
isNullOrEmpty(a) && isNullOrEmpty(b)

The above conditions fail during evaluation because MVELRoutingRule uses an immutable map.

java.lang.UnsupportedOperationException
	at com.google.common.collect.ImmutableMap.put(ImmutableMap.java:813)
	at org.mvel2.integration.impl.CachingMapVariableResolverFactory.externalize(CachingMapVariableResolverFactory.java:101)
	at org.mvel2.MVEL.executeExpression(MVEL.java:988)
	at io.trino.gateway.ha.router.MVELRoutingRule.evaluateCondition(MVELRoutingRule.java:116)
	at io.trino.gateway.ha.router.FileBasedRoutingGroupSelector.lambda$findRoutingDestination$1(FileBasedRoutingGroupSelector.java:83)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
	at io.trino.gateway.ha.router.FileBasedRoutingGroupSelector.findRoutingDestination(FileBasedRoutingGroupSelector.java:82)
	at io.trino.gateway.ha.router.TestRoutingGroupSelector.testTrinoQueryPropertiesNoRouting(TestRoutingGroupSelector.java:168)
	at java.base/java.lang.reflect.Method.invoke(Method.java:580)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1597)