Accounting for situations where '-' symbol is returned for null numeric values

[edmundas-kevisas]

Example API response that is handled with the PR change:

...
"line_items": [
    {
        ...
        "taxes": [
            {
                "id": 1,
                "total": "-",
                "subtotal": "-"
            }
        ],
        ...
    }
],
...