Space in check box export value

[cbgithub2]

check box export value with space set_field threw error message.

Unhandled Java Exception in create_output(): java.lang.ClassCastException: pdftk.com.lowagie.text.pdf.PdfNull cannot be cast to pdftk.com.lowagie.text.pdf.PdfDictionary at pdftk.com.lowagie.text.pdf.FdfReader.readFields(FdfReader.java:146) at pdftk.com.lowagie.text.pdf.FdfReader.readPdf(FdfReader.java:117) at pdftk.com.lowagie.text.pdf.PdfReader.(PdfReader.java:172) at pdftk.com.lowagie.text.pdf.PdfReader.(PdfReader.java:161) at pdftk.com.lowagie.text.pdf.FdfReader.(FdfReader.java:74) at com.gitlab.pdftk_java.TK_Session.create_output(TK_Session.java:2717) at com.gitlab.pdftk_java.pdftk.main_noexit(pdftk.java:156) at com.gitlab.pdftk_java.pdftk.main(pdftk.java:128) There was a problem with pdftk-java. Please report it at https://gitlab.com/pdftk-java/pdftk/issues including the message above, the version of pdftk-java (3.0.6), and if possible steps to reproduce the error.