static get instance() {
        const s = Symbol.for('pgPromiseQueryFile');
        let scope = global[s];
        if (!scope) {
            scope = {
                usedPath: {} // used-path look-up dictionary
            };
            global[s] = scope;
        }
        return scope;
    }
Global instance of the file-path repository.

@return {{usedPath: {}}}