v1.4.3 — Fields a document doesn't have no longer export as 0

Documents in one Firestore collection can carry different fields, and the console leaves those cells blank. Firexport wrote 0 into them — CSV and JSON, both plans — so a real 0 was indistinguishable from a field the document never had. Blank cells now export as empty.

• Documents whose fields are all empty strings are no longer dropped from the file.

• A field named toString or constructor no longer exports a JavaScript function.

• In JSON an absent field is written as "", not omitted.