Hide plugin preference page depending on if plugin is installed (why doesn't this work?)

plugin.xml

<extension point="org.eclipse.ui.propertyPages">
    <page id="com.example.ProjectPreferencesPage"
        class="com.example.MyProjectPreferencePage"
        category="my-category"
        name="Exaple">
        <hiddenWhen>
            <adapt type="org.eclipse.core.runtime.Platform">
                <with variable="platform">                        
                    <test property="org.eclipse.core.runtime.isBundleInstalled" args="some.other.plugin"/>                       
                 </with>
              </adapt>
        </hiddenWhen>
    </page>
</extension>