Write iBatis dynamic query that returns results only when atleast one parameter is sent

iBatis allows building dynamic query conditionally based on properties sent to the named SQL. Suppose We have a Person implementation where the search page allows search by id or by email id (assuming both are unique). We could write two queries

<select id="getPersonById" resultClass="Person" >
select * from PERSON where ID = #value#
</select>

<select id="getPersonByManagerId"  resultClass="Person" >
select * from PERSON where EMAIL_ID = #value#
</select>

OR we could make a dynamic Query like the following

<select id="getPerson"  resultClass="Person" parameterClass="java.util.map">
select * from PERSON 
<dynamic prepend="where" >
<isNotNull parameter="id">
 ID = #id#
</isNotNull>
<isNotNull parameter="managerId">
 EMAIL_ID = #emailId#
</isNotNull>
</dynamic>
</select>

However there is one pitfall. If the parameter does not contain either id or managerId, we are going to return all Person objects and a java queryForObject will throw a multiple objects found exception. How do we avoid this? One solution is to add a or condition with a ubiquitous false expression

something like this

<select id="getPerson"  resultClass="Person" parameterClass="java.util.map">
select * from PERSON where 1=0 
<dynamic prepend="or" >
<isNotNull parameter="id">
 ID = #id#
</isNotNull>
<isNotNull parameter="managerId" prepend="and" >
 EMAIL_ID = #emailId#
</isNotNull>
</dynamic>
</select>

if both parameters are null, the statement will never return any result-sets so we are good. And notice that if BOTH filters are given, it would AND and still return only one result.