Check schema w/o string fields using GraphiQL validators

[Totktonada]

I suspect we can get pcre argument with no fields, then convert it to graphql InputObject and expose.

[Totktonada]

It also worth to check uppermost filters with a collection that does not have comparable fields: say, only float and double.

[Totktonada]

It fails on the following GraphiQL check:

28909     !(fieldNames.length > 0) ? (0, _invariant2.default)(0, this.name + ' fields must be an object with field names as keys or a ' + 'function which returns such an object.') : void 0;