It seems to me there is a bug in ClosedXML.Excel.CalcEngine.Text.Left method.
In an excel cell, if we write formula:
```
=LEFT(A1)
```
and when A1 cell contains empty string, it fails:
> System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.
Parameter name: length
at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy)
at ClosedXML.Excel.CalcEngine.Text.Left(List`1 p)
Before calling String,Substring, there should be some code to return the p[0] string if n is greater than p[0] length.
In an excel cell, if we write formula:
```
=LEFT(A1)
```
and when A1 cell contains empty string, it fails:
> System.ArgumentOutOfRangeException: Index and length must refer to a location within the string.
Parameter name: length
at System.String.InternalSubStringWithChecks(Int32 startIndex, Int32 length, Boolean fAlwaysCopy)
at ClosedXML.Excel.CalcEngine.Text.Left(List`1 p)
Before calling String,Substring, there should be some code to return the p[0] string if n is greater than p[0] length.