mybatis-error

ERR#1:target is null for method size

Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error updating database.  Cause: java.lang.NullPointerException: target is null for method size
### Cause: java.lang.NullPointerException: target is null for method size
    at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:26)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:154)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.apache.ibatis.session.SqlSessionManager$SqlSessionInterceptor.invoke(SqlSessionManager.java:285)
    at $Proxy18.update(Unknown Source)
    at org.apache.ibatis.session.SqlSessionManager.update(SqlSessionManager.java:206)
    at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:54)
    at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:52)
    at $Proxy26.saveAlarmDetailReadBatch(Unknown Source)
    at com.jimi.tracker.api.ApiServlet.saveAlarmDetailRead(ApiServlet.java:719)
    ... 28 more
Caused by: java.lang.NullPointerException: target is null for method size
    at org.apache.ibatis.ognl.OgnlRuntime.callMethod(OgnlRuntime.java:862)
    at org.apache.ibatis.ognl.ASTMethod.getValueBody(ASTMethod.java:73)
    at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
    at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
    at org.apache.ibatis.ognl.ASTChain.getValueBody(ASTChain.java:109)
    at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
    at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
    at org.apache.ibatis.ognl.ASTGreater.getValueBody(ASTGreater.java:49)
    at org.apache.ibatis.ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:170)
    at org.apache.ibatis.ognl.SimpleNode.getValue(SimpleNode.java:210)
    at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:333)
    at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:413)
    at org.apache.ibatis.ognl.Ognl.getValue(Ognl.java:395)
    at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:48)
    at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateBoolean(ExpressionEvaluator.java:32)
    at org.apache.ibatis.scripting.xmltags.IfSqlNode.apply(IfSqlNode.java:33)
    at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:32)
    at org.apache.ibatis.scripting.xmltags.TrimSqlNode.apply(TrimSqlNode.java:54)
    at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:32)
    at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:40)
    at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:278)
    at org.apache.ibatis.executor.statement.BaseStatementHandler.<init>(BaseStatementHandler.java:64)
    at org.apache.ibatis.executor.statement.PreparedStatementHandler.<init>(PreparedStatementHandler.java:39)
    at org.apache.ibatis.executor.statement.RoutingStatementHandler.<init>(RoutingStatementHandler.java:45)
    at org.apache.ibatis.session.Configuration.newStatementHandler(Configuration.java:468)
    at org.apache.ibatis.executor.SimpleExecutor.doUpdate(SimpleExecutor.java:46)
    at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:105)
    at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:71)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:152)
    ... 39 more

錯誤原因：
sqlmapper文件如下：

<update  id="saveAlarmDetailReadBatch"  parameterType="Map">
        UPDATE alarm_info SET read_status=0
        <where>
            <if test="imeis.size()  > 0">
                <foreach collection="imeis"  item="item" separator=" or " open="and (" close=")">
                    imei = #{item}
                </foreach>
            </if>

        </where>
</update>

當入參中未傳入imeis參數時，mybatis調用imeis.size()會報如上錯誤

解決辦法：
將判斷條件改爲：test=”imeis !=null and imeis.size() “