localePatternPaths should never be null, no need to check. (nowhere else in the class is it checked against null, ideally the field should have been final).

just `if ( localePatternPaths.get(customizationKey) != null )` please.

it's also important (as is typically for apache projects) that the code style is exact.
that is: use braces on if statements, and a space between parenthesis and brace, eg `) {`

otherwise the pull request is spot on.