@Nullable
  T importScheme(@NotNull Project project,
                 @NotNull VirtualFile selectedFile,
                 @NotNull T currentScheme,
                 @NotNull SchemeFactory<? extends T> schemeFactory) throws SchemeImportException;
@Nullable
  T importScheme(@NotNull Project project,
                 @NotNull VirtualFile selectedFile,
                 @NotNull T currentScheme,
                 @NotNull SchemeFactory<? extends T> schemeFactory)