✅ how to avoid string.Join with empty strings?

I have

List<IdentifierDto> Identifiers

List<IdentifierDto> Identifiers

and I'm trying to get

Title

Title

from

Identifiers

Identifiers

my code:

 Identifier: subject.Identifiers?
           .Select( identifier => identifier?.Title )
           .JoinToString( "," )

 Identifier: subject.Identifiers?
           .Select( identifier => identifier?.Title )
           .JoinToString( "," )

some times I get result: "," and I don't understand how can I fix this