@Nullable
  CompilerDirectHierarchyInfo getDirectInheritors(@NotNull PsiNamedElement aClass,
                                                  @NotNull GlobalSearchScope searchScope,
                                                  @NotNull FileType searchFileType);
@Nullable
  CompilerDirectHierarchyInfo getDirectInheritors(@NotNull PsiNamedElement aClass,
                                                  @NotNull GlobalSearchScope searchScope,
                                                  @NotNull FileType searchFileType)