default @Nullable @Nls String getAssignabilityExplanation(@NotNull TypeConstraint otherType,
                                                            boolean expectedAssignable,
                                                            @Nls String elementTitle) {
    return null;
  }
default @Nullable @Nls String getAssignabilityExplanation(@NotNull TypeConstraint otherType,
                                                            boolean expectedAssignable,
                                                            @Nls String elementTitle)