java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringEscapeUtils (when using dump_data_utf8)

pdftk combined/application-huettel.pdf dump_data_utf8 > combined/application-huettel.data
Unhandled Java Exception in create_output():
java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringEscapeUtils
        at com.gitlab.pdftk_java.report.OutputXmlString(report.java:61)
        at com.gitlab.pdftk_java.report.OutputPdfName(report.java:92)
        at com.gitlab.pdftk_java.report.ReportInfo(report.java:810)
        at com.gitlab.pdftk_java.report.ReportOnPdf(report.java:964)
        at com.gitlab.pdftk_java.TK_Session.create_output(TK_Session.java:3365)
        at com.gitlab.pdftk_java.pdftk.main(pdftk.java:177)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang3.StringEscapeUtils
        at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
        ... 6 more

Happy to help debugging. The raw file used here is confidential though, I'd have to come up with a minimal reproducer. Also, java n00b.