I am getting a NPE on executing query using joins -

Mapping:-
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>

<class name="com.xx.apps.xpmkz.datalayer.XPMKZData" table="XPMKZ">
<composite-id name="XPMKZID" class="com.xx.apps.xpmkz.datalayer.XPMKZID">
<key-property name="CPN"
column="CPN"/>
<key-property name="Type"
column="TYPE"/>
<key-property name="Station"
column="STATION"/>
<key-property name="Sublocation"
column="SUBLOCATION"/>
</composite-id>
<property name="Value" type="int" column="VALUE"/>
<property name="UpdateDate" type="timestamp" column="UPDATE_DATE"/>
<property name="SentDate" type="timestamp" column="SENT_DATE"/>
<property name="SentStatus" type="int" column="SENT_STATUS"/>
</class>

</hibernate-mapping>
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Query String -
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"select t1, t2 " +
"from XPMKZData as t1 " +
"left join fetch com.xx.apps.xpmkz.datalayer.XPMKZData as t2 " +
"where t1.XPMKZID.CPN = t2.XPMKZID.CPN " +
"and t1.XPMKZID.Station = t2.XPMKZID.Station " +
"and t1.XPMKZID.Sublocation = t2.XPMKZID.Sublocation " +
"and t1.XPMKZID.Station=? " +
"and t1.XPMKZID.Sublocation=? ";
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HSQL -
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select t1, t2 from com.xx.apps.xpmkz.datalayer.XPMKZData as t1 left join fetch com.xx.apps.xpmkz.datalayer.XPMKZData as t2 where t1.XPMKZID.CPN = t2.XPMKZID.CPN and t1.XPMKZID.Station = t2.XPMKZID.Station and t1.XPMKZID.Sublocation = t2.XPMKZID.Sublocation and t1.XPMKZID.Station=? and t1.XPMKZID.Sublocation=?
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Exception
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java.lang.NullPointerException
at org.hibernate.hql.ast.HqlSqlWalker.createFromJoinElement(HqlSqlWalker.java:332)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.joinElement(HqlSqlBaseWalker.java:3275)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElement(HqlSqlBaseWalker.java:3067)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromElementList(HqlSqlBaseWalker.java:2945)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.fromClause(HqlSqlBaseWalker.java:688)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:544)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:281)
at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:229)
at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:251)
at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:183)
at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:134)
at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:101)
at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:94)
at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:156)
at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:135)
at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1650)
at com.xx.apps.xpmkz.dbservices.XPMKZDao.getSublocationMKZrecords(XPMKZDao.java:155)
at tests.com.xx.apps.xpmkz.dbservices.XPMKZDaoTest.testGetSublocationRecords(XPMKZDaoTest.java:116)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at junit.framework.TestCase.runTest(TestCase.java:164)
at junit.framework.TestCase.runBare(TestCase.java:130)
at junit.framework.TestResult$1.protect(TestResult.java:106)
at junit.framework.TestResult.runProtected(TestResult.java:124)
at junit.framework.TestResult.run(TestResult.java:109)
at junit.framework.TestCase.run(TestCase.java:120)
at junit.framework.TestSuite.runTest(TestSuite.java:230)
at junit.framework.TestSuite.run(TestSuite.java:225)
at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:128)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

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