Extensions can be configured with an external XML file (and not "inline"), as follows:

<extension-point id="org.ametys.web.inputdata.InputDataExtensionPoint"
                 class="org.ametys.web.inputdata.InputDataExtensionPoint"
                 config="/WEB-INF/param/inputdata.xml">
</extension-point>

When configured this way, the extension requires the file to exist, or it crashes when the application initializes.
In my opinion, it should not crash, and the configure(Configuration conf) method should be passed an "empty" Configuration object. The Component itself should decide if it has enough input to be correctly configured, and throw a ConfigurationException if it doesn't, as it's done with "inline" configuration.