Zip encode with password creates a "Null check operator used on a null value"

[tototo23]

When using

ZipFileEncoder(password: .....).zipDirectory(directory, ...);

To zip a folderhaving subfolders, with a password, i have a Null exception. Following the exception, it reveals that it comes from zip_encoder:355 : output.writeBytes(salt!); having salt==null. This is called from _writeFile() line 261,where salt is not initialized in this context, when the current object is a Folder and not a File