Tomcat: how to set an XML attribute in context.xml as null?

Question

I would like to dynamically configure sessionCookieDomain as an environment variable. In my context.xml, I have:

<Context sessionCookieDomain="${environment.sessionCookieDomain}">
...
</Context>

given that the environment.sessionCookieDomain is a configuration property.

I would like to only set it in certain conditions, otherwise, leave it to default (which is null). Is that possible?