question: @ NotNull public List < Pair < C , Collection < VirtualFile > > > createConfigurations ( @ NotNull Collection < VirtualFile > files , @ NotNull Collection < C > existentFacetConfigurations ) { final C configuration = createConfiguration ( files ) ; if ( configuration != null ) { return Collections . singletonList ( Pair . create ( configuration , files ) ) ; } return Collections . emptyList ( ) ; }
target:  Override this method if several facets of this type are allowed in a single module