Premise

Knowledge of statically typed languages with null or equivalent functionality
See the following article for definitions of null-tolerant, null-tolerant, and null-tolerant safe types
Comparison of non-nullable type, nullable non-safety type, and nullable safe type from the viewpoint of null safety -Qiita

problem

Why null is said to be bad

Short answer

null itself is not bad. It can be said that there are cases where the nullable unsafe type is also convenient for limited use. The bad news is that languages have made nullable unsafe types the default types (eg Java, C #, Objective-C). Such languages unnecessarily run the risk of run-time exceptions as a result of abusing nullable and unsafe types.

[^ 10]: Almost agree with the next article null unsafe languages are no longer legacy languages -Qiita

Long answer

TBW

reference

[Tony Hoare -Wikipedia](https://ja.wikipedia.org/wiki/%E3%82%A2%E3%83%B3%E3%83%88%E3%83%8B%E3%83 % BC% E3% 83% BB% E3% 83% 9B% E3% 83% BC% E3% 82% A2) Inventor with reference to Null
null insecure languages are no longer legacy languages -Qiita