The null value has a special meaning in computer science, it is used to declare that a value is not yet defined, known or exist. The speciality of null is, that altough it shows us that a value is missing, it is itself a value. So it is possible to compare two non existing values. For example null is useful for databases. Suppose we have a database of patient, it does make a different if a patient has not a disease (0) or is not yet diagnosed (null).
I do not like the image, hopefully someone has a better idea. Also the notation of null (or NULL) and include NaN etc.?
TS, 28.03.2019
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