leave out "Tweets by" when ${TWITTER} is empty

[KonradHoeffner]

Our project does not have a Twitter account, however when I set TWITTER= (empty string) in .env, "Tweets by" still shows up on the index page even though there are no tweets below.
Is there a way to hide the "Tweets by" text or if not, could you change the code of ols-web so that it will be automatically hidden when the variable is empty?