Scala: combining two different maps with a common key

https://stackoverflow.com/questions/9641102/how-to-merge-two-maps-into-one-with-keys-from-the-first-map-and-merged-values?noredirect=1&lq=1

Code:
https://scalafiddle.io/sf/03fEQqi/2

The value of map1 contains a key in map 2.

Lets combine the two maps using the common key.