当查询成功找到两个节点时，它可以返回一些东西（比如新的关系），而不是错误。如果查询不返回任何内容，则意味着一个或两个节点都不存在。
举例来说：

MATCH (user1: User{uuid: '123'}), (user2: User{uuid: '456'})
CREATE (user1)-[r:LIKES]->(user2)
RETURN r;

我想这样的东西会起作用：

OPTIONAL MATCH (user1: User{uuid: '123'})
WITH user1, CASE WHEN user1 IS NULL THEN true ELSE FALSE END AS nodeNotFound
CALL apoc.util.validate(nodeNotFound,'User 1 with given property and label not found!', [404]) 
OPTIONAL MATCH (user2: User{uuid: '456'})
WITH user1, user2, CASE WHEN user2 IS NULL THEN true ELSE FALSE END AS nodeNotFound
CALL apoc.util.validate(nodeNotFound,'User 2 with given property and label not found!', [404])
WITH user1,user2
MERGE (user1)-[:LIKES]->(user2)