[BUG] GOpt fails in compiling queries that involve ISNULL on certain properties

[BingqingLyu]

Describe the bug

In the JOB Benchmark, the gopt-based compiler fails to compile queries that involve ISNULL on certain properties, including Job11, 21, and 27.

The issue arises because the graph schema does not inform the compiler that certain properties can be optional. As a result, the compiler treats these properties as non-nullable.

Take Job11a as an example, currently the compiler returns a null.

@neo4j> MATCH
        (mc:MOVIE_COMPANIES)-[:MOVIE_COMPANIES_TITLE]->(t:TITLE)-[:MOVIE_KEYWORD]->(k:KEYWORD),
        (mc)-[:MOVIE_COMPANIES_COMPANY_NAME]->(cn:COMPANY_NAME),
        (mc)-[:MOVIE_COMPANIES_TYPE]->(ct:COMPANY_TYPE),
        (t)<-[:MOVIE_LINK_TITLE]-(ml:MOVIE_LINK)-[:MOVIE_LINK_LINKED_TYPE]->(lt:LINK_TYPE)
        WHERE cn.country_code <> '[pl]'
          AND (cn.name CONTAINS 'Film' OR cn.name CONTAINS 'Warner')
          AND ct.kind = 'production companies'
          AND k.keyword = 'sequel'
          AND lt.link CONTAINS 'follow'
          AND mc.note IS NULL
          AND t.production_year >= 1950
          AND t.production_year <= 2000
        RETURN
          MIN(cn.name) AS from_company,
          MIN(lt.link) AS movie_link_type,
          MIN(t.title) AS non_polish_sequel_movie;
null