cypher - Neo4j: when merging does not overwrite node properties -

i want modify merge cypher query property field not overwritten.

to update node properties use following cypher query:

merge (n:person {name:"me"}) on match set n+={id:"2"} on create set n={name:"me", id="1"} return n

if call same query again on match set n+={id:"3"} id updated.

how make query adds property if not existing not overwrite if present?

first, can use plain properties, no need {map}..

secondly, in case merge creates node, have property name:me on :

merge (n:person {name:'me'}) on match set n.id = 2 on create set n.id = 1 return n