PDFAnnotation check if the signature is filled

Hi,

I try to check which signature fields annotations are filed in.

I tried to get some values from the annotation but I can't tell if the signature field is filled.

I only found one thing. If signature field was filled annot.widgetStringValue return empty string ("").

If the field wasn't filled, annot.widgetStringValue return nil.

Here is me code:

private func setupAnnotation(page: PDFPage) {
        for annot in page.annotations {
            
            if annot.widgetFieldType == .button {
                
            }
            else if annot.widgetFieldType == .choice {
                
            }
            else if annot.widgetFieldType == .signature {
                let value = annot.value(forAnnotationKey: .widgetValue)
                print(value)
                
                print(annot.widgetStringValue)
                
                print(annot.accessibilityValue)
                print(annot.annotationKeyValues)
            }
            else if annot.widgetFieldType == .text {
                
            }
           
        }
    }

There is no property such as "isFilled", or "isSigned", or "hasValue".

How can I check if signature field is filled?