Sonar-custom-rules-examples/java-custom-rules unit testcases failed Caused by: org.sonar.sslr.grammar.GrammarException

I run the sonar-custom-rules-examples\java-custom-rules(code clone from github https://github.com/SonarSource/sonar-custom-rules-examples/master ) unit testcases, and testcases all failed because of following exception.(<sslr.version>1.21</sslr.version>)

exception detail:
java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at com.google.common.base.Throwables.propagate(Throwables.java:160)
at com.sonar.sslr.impl.typed.ReflectionUtils.invokeMethod(ReflectionUtils.java:38)
at com.sonar.sslr.api.typed.ActionParser.(ActionParser.java:79)
at org.sonar.java.ast.parser.JavaParser.(JavaParser.java:37)
at org.sonar.java.ast.parser.JavaParser.createParser(JavaParser.java:41)
at org.sonar.java.ast.JavaAstScanner.scanSingleFileForTests(JavaAstScanner.java:136)
at org.sonar.java.checks.verifier.JavaCheckVerifier.scanFile(JavaCheckVerifier.java:280)
at org.sonar.java.checks.verifier.JavaCheckVerifier.scanFile(JavaCheckVerifier.java:267)
at org.sonar.java.checks.verifier.JavaCheckVerifier.scanFile(JavaCheckVerifier.java:221)
at org.sonar.java.checks.verifier.JavaCheckVerifier.verify(JavaCheckVerifier.java:105)
at org.sonar.samples.java.checks.AvoidAnnotationCheckTest.detected(AvoidAnnotationCheckTest.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:69)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:48)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
at org.junit.runners.ParentRunner.run(ParentRunner.java:292)
at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.sonar.sslr.impl.typed.ReflectionUtils.invokeMethod(ReflectionUtils.java:36)
… 31 more
Caused by: org.sonar.sslr.grammar.GrammarException: The rule ‘f.newTuple20(Object, Object)’ has already been defined somewhere in the grammar.
at org.sonar.sslr.grammar.GrammarBuilder$RuleBuilder.is(GrammarBuilder.java:285)
at com.sonar.sslr.impl.typed.GrammarBuilderInterceptor.replaceByRule(GrammarBuilderInterceptor.java:159)
at com.sonar.sslr.api.typed.ActionParser$ActionMethodInterceptor.intercept(ActionParser.java:138)
at org.sonar.java.ast.parser.TreeFactory$$EnhancerByCGLIB$$311c1427.newTuple20()
at org.sonar.java.ast.parser.JavaGrammar.ARGUMENTS(JavaGrammar.java:1394)
at org.sonar.java.ast.parser.JavaGrammar$$EnhancerByCGLIB$$baf8498a.CGLIB$ARGUMENTS$123()
at org.sonar.java.ast.parser.JavaGrammar$$EnhancerByCGLIB$$baf8498a$$FastClassByCGLIB$$ba9b31ec.invoke()
at net.sf.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
at com.sonar.sslr.impl.typed.GrammarBuilderInterceptor.intercept(GrammarBuilderInterceptor.java:76)
at org.sonar.java.ast.parser.JavaGrammar$$EnhancerByCGLIB$$baf8498a.ARGUMENTS()
… 36 more