Refactoring to functional programming in Java 8

Specification

• The search for participants by first name in the list of members of the meetup should :
  • Return no participant where there is no member found with the query.
  • Return one participant when there is a member found with the query.
  • Return all matching participants where there are multiple members found with the query.

Exercice

Refactoring the production code so that becomes functional.