TotalDebt sometimes returns `null`

[Matthiee]

At the moment the field for totalDebt is not nullable.

FinancialModelingPrep.NET/FinancialModelingPrepApi/Model/CompanyValuation/BalanceSheetResponse.cs

Line 158 in 5a9129b

public double TotalDebt { get; set; }

Sometimes FMP API returns null for this field.

I created a support ticket to check if this is valid or not.