GetFormFieldValue not working for one signature

I have trouble finding out if a given signature field is signed. 

I tried all methods that have the prefix "getFormField" and compared them with a form field that has a value filled through Debenu on iOS and also with an empty form field. 

The "getFormFieldValue" method returns no value for the first signature field (returned nil). For the second signature field returns its value (string of contents), and for the last, empty, signature field returns empty string (returned "").

How do I find out that the first signature field is filled?

link to pdf file: http://drive.google.com/open?id=1he-vzcKleX9eovsnnhrGk53JNLTCKYKf

all methods I try to call:

 var val = [String?]()

 val.append(String(_dqpl.getFormFieldAlignment(id)))

 val.append(String(_dqpl.getFormFieldAnnotFlags(id)))

 val.append(String(_dqpl.getFormFieldBackgroundColorType(id)))

 val.append(String(_dqpl.getFormFieldBorderColorType(id)))

 val.append(String(_dqpl.getFormFieldBorderStyle(id)))

 val.append(String(_dqpl.getFormFieldCaption(id)))

 val.append(String(_dqpl.getFormFieldCaptionEx(id, 1)))

 val.append(String(_dqpl.getFormFieldCaptionEx(id, 2)))

 val.append(String(_dqpl.getFormFieldCaptionEx(id, 3)))

 val.append(String(_dqpl.getFormFieldCheckStyle(id)))

 val.append(String(_dqpl.getFormFieldChildTitle(id)))

 val.append(String(_dqpl.getFormFieldChoiceType(id)))

 val.append(String(_dqpl.getFormFieldComb(id)))

 val.append(String(_dqpl.getFormFieldDefaultValue(id)))

 val.append(String(_dqpl.getFormFieldDescription(id)))

 val.append(String(_dqpl.getFormFieldFlags(id)))

 val.append(String(_dqpl.getFormFieldFontName(id)))

 val.append(String(_dqpl.getFormFieldKidCount(id)))

 val.append(String(_dqpl.getFormFieldKidTempIndex(id, 1)))

 val.append(String(_dqpl.getFormFieldMaxLen(id)))

 val.append(String(_dqpl.getFormFieldNoExport(id)))

 val.append(String(_dqpl.getFormFieldPage(id)))

 val.append(String(_dqpl.getFormFieldPrintable(id)))

 val.append(String(_dqpl.getFormFieldReadOnly(id)))

 val.append(String(_dqpl.getFormFieldRequired(id)))

 val.append(String(_dqpl.getFormFieldRichTextString(id, "RV")))

 val.append(String(_dqpl.getFormFieldRichTextString(id, "DS")))

 val.append(String(_dqpl.getFormFieldRotation(id)))

 val.append(String(_dqpl.getFormFieldSubCount(id)))

 val.append(String(_dqpl.getFormFieldSubName(id, 1)))

 val.append(String(_dqpl.getFormFieldSubmitActionString(id, "U")))

 val.append(String(_dqpl.getFormFieldTabOrder(id)))

 val.append(String(_dqpl.getFormFieldTabOrderEx(id, 0)))

 val.append(String(_dqpl.getFormFieldTabOrderEx(id, 1)))

 val.append(String(_dqpl.getFormFieldTextSize(id)))

 val.append(String(_dqpl.getFormFieldTitle(id)))

 val.append(String(_dqpl.getFormFieldType(id)))

 val.append(String(_dqpl.getFormFieldVisible(id)))

 val.append(String(_dqpl.getFormFieldValue(id)))

results:

- the first result is for the first signature that is signed, but Debenu does not display its value.

- the second result is for the signature which is signed via Debenu and the value is correct

- the third result for the blank, unsigned signature field

first:

["0", "132", "0", "0", "0", "", "", "", "", "8", "Signature_ios_1", "0", "0", "", "", "0", "Helvetica", "0", "0", "0", "0", "1", "1", "0", "0", "", "", "0", "0", "", "", "1", "1", "1", "10.0", "Signature_ios_1", "6", "1", "nil"]

second:

["0", "4", "0", "0", "0", "", "", "", "", "8", "Signature_ios_2", "0", "0", "", "", "0", "Helvetica", "0", "0", "0", "0", "1", "1", "0", "0", "", "", "0", "0", "", "", "2", "2", "2", "10.0", "Signature_ios_2", "6", "1", "<<\n/Type /Sig\n/Filter /Adobe.PPKLite\n/SubFilter /adbe.pkcs7.detached\n/Contents <308205A206092A864886F70D010702A082059330820....... ......\n>>\n"]

third:

["0", "4", "0", "0", "0", "", "", "", "", "8", "Signature_ios_3", "0", "0", "", "", "0", "Helvetica", "0", "0", "0", "0", "1", "1", "0", "0", "", "", "0", "0", "", "", "3", "3", "3", "10.0", "Signature_ios_3", "6", "1", ""]