map.merge

flex.map.merge(map1, map2, ...)

WITH {a: 1, b: 2} AS map1, {b: 3, c: 4} AS map2
RETURN flex.map.merge(map1, map2) AS result

result
------------------
{a: 1, b: 3, c: 4}

MATCH (u:User {id: 123})
WITH {role: 'admin', status: 'active'} AS defaults
RETURN flex.map.merge(defaults, properties(u)) AS userWithDefaults

WITH {host: 'localhost', port: 6379} AS defaults,
     {port: 7000, password: 'secret'} AS config
RETURN flex.map.merge(defaults, config) AS finalConfig

finalConfig
--------------------------------------------------
{host: 'localhost', port: 7000, password: 'secret'}

WITH {a: 1} AS base, {b: 2} AS extra1, {c: 3} AS extra2
RETURN flex.map.merge(base, extra1, extra2) AS combined