hibernate hql case when 子查询报java.lang.NullPointerException错误

hql语句大致如下

select t, case when t.targetType=0 then   
(select a.name from MarketApp a where a.id = t.target )    
else '' end  
from ThemeComponent t where t.theme.id = 1 

jsp报如下错误

java.lang.NullPointerException  
    at org.hibernate.hql.internal.ast.tree.CaseNode.getDataType(CaseNode.java:39)  
    at org.hibernate.hql.internal.ast.tree.SelectClause.initializeExplicitSelectClause(SelectClause.java:152)  
    at org.hibernate.hql.internal.ast.HqlSqlWalker.useSelectClause(HqlSqlWalker.java:859)  
    at org.hibernate.hql.internal.ast.HqlSqlWalker.processQuery(HqlSqlWalker.java:649)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:663)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:299)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:247)  
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:248)  
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:183)  
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:136)  
    at org.hibernate.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:105)  
    at org.hibernate.engine.query.spi.HQLQueryPlan.(HQLQueryPlan.java:80)  
    at org.hibernate.engine.query.spi.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:168)  
    at org.hibernate.internal.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:221)  
    at org.hibernate.internal.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:199)  
    at org.hibernate.internal.SessionImpl.createQuery(SessionImpl.java:1777)  

后台控制台报如下错误

[2014-06-12 09:29:37 ERROR] [http-8080-3] org.hibernate.hql.internal.ast.ErrorCounter.reportError(50) | <AST>:0:0: unexpected AST node: query  
<AST>:0:0: unexpected AST node: query  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.expr(HqlSqlBaseWalker.java:1363)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.caseExpr(HqlSqlBaseWalker.java:5074)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.arithmeticExpr(HqlSqlBaseWalker.java:3199)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectExpr(HqlSqlBaseWalker.java:2332)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectExprList(HqlSqlBaseWalker.java:2145)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectClause(HqlSqlBaseWalker.java:1451)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:571)  
    at org.hibernate.hql.internal.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:299)  

org.hibernate.hql.internal.ast.tree.CaseNode.getDataType(CaseNode.java:39) 可以看出 报错是因为hibernate不知道子查询返回的是什么类型，所以报错，那就强制让它知道，比如本例子返回的是字符串类型，所以可以改成如下

select t, case when t.targetType=0 then   
((select a.name from MarketApp a where a.id = t.target )  || '')   
else '' end  
from ThemeComponent t where t.theme.id = 1