Check if a property exists in oozie EL workflow

Question

I am trying to set a property based on the existence of another property in the oozie workflow.xml file as follows:

<global>
    <configuration>
        <property>
            <name>outputTableName</name>
            <value>${firstNotNull(inputTableName, outputTableOverride)}</value>
        </property>
    </configuration>
</global>

But, outputTableOverride exists only in some cases. Therefore, it fails because it is sometimes absent. Is there a way to check if a property exists?