Shared coding conventions allow teams to collaborate effectively. While types for lambda arguments are optional, specifying them anyway makes the code clearer and easier to read.
Arrays.sort(rosterAsArray, (a, b) -> { // Noncompliant return a.getBirthday().compareTo(b.getBirthday()); } );
Arrays.sort(rosterAsArray, (Person a, Person b) -> { return a.getBirthday().compareTo(b.getBirthday()); } );