null

null is used to represent missing/undefined values.
null is not equal to null. Not knowing two values does not imply that they are the same value. So the expression null = null yields null and not true. To check if an expression is null, use IS NULL.
Arithmetic expressions, comparisons and function calls (except coalesce) will return null if any argument is null.
An attempt to access a missing element in a list or a property that doesnât exist yields null.
In OPTIONAL MATCH clauses, nulls will be used for missing parts of the pattern.

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