swagger-parser-v3 failed on Windows for relative $ref

On Windows for swagger-parver-v3 v2.0.24, we have StringIndexOutOfBoundsException for relative $ref like
$ref: './path/file.yaml#/components/schemas/Type'

Parsing problem is on ExternalRefProcessor.processRefToExternalSchema at line 113
String parent = file.substring(0, file.lastIndexOf(File.separatorChar));

I don't think that OS specific separator need to be use here.
In yaml, all paths are with '/' no ?
I think only lastIndexOf '/' is needed :
String parent = file.substring(0, file.lastIndexOf('/'));

But after this change, we have other problem on :
schemaFullRef = Paths.get(parent, schemaFullRef).normalize().toString();

After normalise relative in file part "#/components/schemas/Type" is also convert to :
path\file.yaml#\components\schemas\Type

I made some change for adjust that with :

if (schemaFullRef.contains("#/")) {
    String[] parts = schemaFullRef.split("#/");
    String schemaFullRefFilePart = parts[0];
    String schemaFullRefInternalRefPart = parts[1];
    schemaFullRef = Paths.get(parent, schemaFullRefFilePart).normalize().toString() + "#/" + schemaFullRefInternalRefPart;
} else {
    schemaFullRef = Paths.get(parent, schemaFullRef).normalize().toString();
}

This changes made build OK on Windows and Linux but I'm not sure to cover all case.
Someone see a better approch for a PR ?

Start in ExternalRefProcessor.processRefToExternalSchema around line 113 and trace how relative $ref values are split and normalized. Reproduce the reported relative reference on Windows and Linux, then verify that the file path is normalized without changing the #/components/schemas/Type fragment.