It throw below exception:

Exception in thread "main" java.lang.RuntimeException: Operator 'Operator = 'contains'' does not exist for StringEvaluator
    at org.drools.base.evaluators.StringFactory.getEvaluator(StringFactory.java:70)
    at org.drools.base.ValueType.getEvaluator(ValueType.java:166)
    at org.drools.rule.builder.PatternBuilder.getEvaluator(PatternBuilder.java:900)
    at org.drools.rule.builder.PatternBuilder.buildRestriction(PatternBuilder.java:714)
    at org.drools.rule.builder.PatternBuilder.buildRestriction(PatternBuilder.java:625)
    at org.drools.rule.builder.PatternBuilder.createRestriction(PatternBuilder.java:434)
    at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:308)
    at org.drools.rule.builder.PatternBuilder.buildConstraint(PatternBuilder.java:199)
    at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:168)
    at org.drools.rule.builder.PatternBuilder.build(PatternBuilder.java:93)
    at org.drools.rule.builder.GroupElementBuilder.build(GroupElementBuilder.java:69)
    at org.drools.rule.builder.RuleBuilder.build(RuleBuilder.java:53)
    at org.drools.compiler.PackageBuilder.addRule(PackageBuilder.java:446)
    at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:304)
    at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:167)
    at org.drools.examples.HelloWorldExample.main(HelloWorldExample.java:28)

But if I use a "deep" str field, this issue does not exist, Everything goes well.
The drl is like below:

package org.drools.examples;

import org.drools.examples.HelloWorldExample.Message;

rule "check deep str contains"
    dialect "java"
    when
        m:Message( sec.fir.msg contains "Hello" )
    then
        System.out.println( "===check deep str contains ok===" );
end

It seems a bug, but I am not sure. I attached my test code and the two drl files.
I use below jars to compile and run this test case:

antlr-runtime-3.0.jar
core-3.2.3.v_686_R32x.jar
drools-compiler-4.0.7.jar
drools-core-4.0.7.jar
drools-decisiontables-4.0.7.jar
drools-jsr94-4.0.7.jar
janino-2.5.10.jar
jsr94-1.1.jar
mvel-1.3.12-java1.4.2.jar

Can everyone kindly give me any suggestion?

Thanks!
- Zeke