For the following rule

-----------------------------
package com.sample

import java.util.Map;
import java.util.HashMap;

declare TestFact
@propertyReactive
data : String
end

rule "Test Rule"
when
$fact : TestFact()
then
Map<String,String> a = new HashMap<String,String>();
modify ($fact)

end
------------------------

We get the following exception:

java.lang.RuntimeException: Error while creating KieBase[Message [id=1, level=ERROR, path=rules/Sample.drl, line=11, column=0
text=Unable to resolve type Map<String,String>:
Unable to find class 'Map<String,String>']]
at org.drools.compiler.kie.builder.impl.KieContainerImpl.getKieBase(KieContainerImpl.java:260)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:400)
at org.drools.compiler.kie.builder.impl.KieContainerImpl.newKieSession(KieContainerImpl.java:375)
at com.sample.DroolsTest.main(DroolsTest.java:17)

If we remove the generics, or not using modify(), this has no error.