function sanitizeValue(value) {
    return typeof value === 'string' && sanitizeProjection ? value = 1 : value;
  }
Specifies which document fields to include or exclude (also known as the query "projection")

When using string syntax, prefixing a path with `-` will flag that path as excluded. When a path does not have the `-` prefix, it is included. Lastly, if a path is prefixed with `+`, it forces inclusion of the path, which is useful for paths excluded at the [schema level](https://mongoosejs.com/docs/api/schematype.html#SchemaType.prototype.select()).

A projection _must_ be either inclusive or exclusive. In other words, you must
either list the fields to include (which excludes all others), or list the fields
to exclude (which implies all other fields are included). The [`_id` field is the only exception because MongoDB includes it by default](https://www.mongodb.com/docs/manual/tutorial/project-fields-from-query-results/#suppress-id-field).

#### Example:

    // include a and b, exclude other fields
    query.select('a b');
    // Equivalent syntaxes:
    query.select(['a', 'b']);
    query.select({ a: 1, b: 1 });

    // exclude c and d, include other fields
    query.select('-c -d');

    // Use `+` to override schema-level `select: false` without making the
    // projection inclusive.
    const schema = new Schema({
      foo: { type: String, select: false },
      bar: String
    });
    // ...
    query.select('+foo'); // Override foo's `select: false` without excluding `bar`

    // or you may use object notation, useful when
    // you have keys already prefixed with a "-"
    query.select({ a: 1, b: 1 });
    query.select({ c: 0, d: 0 });

    Additional calls to select can override the previous selection:
    query.select({ a: 1, b: 1 }).select({ b: 0 }); // selection is now { a: 1 }
    query.select({ a: 0, b: 0 }).select({ b: 1 }); // selection is now { a: 0 }


@method select
@memberOf Query
@instance
@param {Object|String|String[]} arg
@return {Query} this
@see SchemaType https://mongoosejs.com/docs/api/schematype.html
@api public