@NotNull
  public static DfaNullability fromDfType(@NotNull DfType type) {
    return type == DfType.FAIL || type instanceof DfPrimitiveType ? NOT_NULL : 
           type instanceof DfReferenceType ? ((DfReferenceType)type).getNullability() : UNKNOWN;
  }
@NotNull
  public static DfaNullability fromDfType(@NotNull DfType type)