What does JD.COM mean by texting that JD.COM is "empty"?

Null means null pointer, which means invalid.

Null is a reserved value in calculation, indicating that the pointer does not point to a valid object. Programs usually use null pointers to indicate conditions, such as the end of an unknown length list or the inability to perform certain operations; The use of this null pointer can be compared with the Nothing value in nullable types and option types.

Because Null is not a data value, but the sign of the missing value, using Null as a mathematical operator will give an unknown result. Because Null is not a member of any data field, it is not regarded as a "value", but a marker (or placeholder) of the missing value. So comparing with Null never leads to true or false, and always becomes in the unknown result of ternary logic.

Extended data:

Different meanings of zero in computer science;

1. null value (SQL)? (NULL), a special flag used to indicate that there are no data values in the database.

2. Empty character, a control character with a value of 0. Many character encodings contain null characters.

3. An empty device is a special device file, which will discard all the data written in it, but will report that the write operation is successful and read it immediately to obtain EOF.

4. Empty modem, also known as empty modem. It is a communication method that uses RS-232 serial cable to directly connect two data terminal devices (without modem).

5. Empty object pattern, a software design pattern.

6. Empty string, zero-length string.

7. Empty termination string, the length of which is determined by the first empty character.

8. Nullable types (a feature of some static programming languages) allow data types to be set to special NULL values.

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