LPS-49928 Validator should be used for null check for strings

I looked for where we check servletContextName == null and replaced them with Validator.isNull()

I also looked at when we use != null, but i think that there might be a few cases for using that instead of Validator.isNotNull() so I left those cases alone (with one exception).

Searching for Validator.isNotNull(servletContextName) brought up a few instances so I think that there may be a reason we left some of the != null cases alone. If I was not sure about a change, I left it alone since this is to prevent errors and not cause them :+1: