Many SessionImpl operations just log a NPE if null values provided

Many operations of SessionImpl require non-null parameters and ensure this by using the checkNotNull method of Google Commons.

If actually provided a null value, it can look like this:

org.apache.sling.engine.impl.SlingRequestProcessorImpl service: Uncaught Throwable
java.lang.NullPointerException: null
    at org.apache.jackrabbit.oak.jcr.session.SessionImpl.getNamespaceURI(SessionImpl.java:788) [org.apache.jackrabbit.oak-jcr:1.42.0]

This NPE because of the failed validation is non-distinguishable from a "regular" NPE. We should use the version of checkNotNull which allows to provide an error string to indicate that the parameter validation failed.