Optional job parameters in Spring Batch

Question

Is it possible make a job parameter optional in the sense that it evaluates to null if it is not specified instead of throwing an exception?

What I'm after is something like a

<bean id="fileNamePattern" class="java.lang.String" scope="step">
    <constructor-arg value="#{jobParameters[fileNamePattern]}" />
</bean>

that I could pass as a property to another bean that handles the case where fileNamePattern is not specified.