Why resource_group_id is varchar type in exact_match_source_selectors? about presto-gateway HOT 1 OPEN

CREATE TABLE IF NOT EXISTS exact_match_source_selectors (
    resource_group_id VARCHAR(128) NOT NULL,  -- WTF varchar?!
    update_time DATETIME NOT NULL,

    -- Selector fields which must exactly match a query
    source VARCHAR(256) NOT NULL, -- (reduced from 512)
    environment VARCHAR(128),
    query_type VARCHAR(128), -- (reduced from 512)

    PRIMARY KEY (environment, source, query_type),
    UNIQUE (source, environment, query_type, resource_group_id)
);