I've been working with Apache FOP for converting XML (held on a BaseX instance) to PDF. Currently this involves saving nodes from the BaseX database to pass into a local FopFactory - not ideal. Have tried to pull one of the documents out and get a 500 error, then tried referencing direct files - which also errors:

import module namespace fop = 'org.basex.modules.fop.FOP';
let $xml := db:open('billing_run_435')/CommercialDocument[@id="203545"] - if returned does show xml
let $xsl := xslt:transform('/home/chris/Downloads/xml/billing_invoice_241040.xml', '/etc/xmlmapper/pdf_invoice.fo') - hard coded for debugging
return $xml

>From the log:

Version: BaseX 8.3.1
Java: Oracle Corporation, 1.7.0_25
OS: Linux, amd64
Stack Trace:
java.lang.NullPointerException
        at org.basex.query.func.xslt.XsltTransform.transform(XsltTransform.java:110)
        at org.basex.query.func.xslt.XsltTransform.transform(XsltTransform.java:59)
        at org.basex.query.func.xslt.XsltTransform.item(XsltTransform.java:37)
        at org.basex.query.expr.ParseExpr.value(ParseExpr.java:64)
        at org.basex.query.QueryContext.value(QueryContext.java:423)
        at org.basex.query.expr.gflwor.Let$LetEval.next(Let.java:187)
        at org.basex.query.expr.gflwor.GFLWOR$1.next(GFLWOR.java:95)
        at org.basex.query.MainModule$1.next(MainModule.java:114)
        at org.basex.query.func.StandardFunc.cache(StandardFunc.java:404)
        at org.basex.query.func.xquery.XQueryEval.eval(XQueryEval.java:129)
        at org.basex.query.func.xquery.XQueryEval.eval(XQueryEval.java:59)
        at org.basex.query.func.xquery.XQueryEval.iter(XQueryEval.java:44)
        at org.basex.query.func.fn.FnSerialize.item(FnSerialize.java:22)
        at org.basex.query.expr.ParseExpr.iter(ParseExpr.java:43)
        at org.basex.query.QueryContext.iter(QueryContext.java:412)
        at org.basex.query.expr.IterMap$1.next(IterMap.java:42)
        at org.basex.query.MainModule$1.next(MainModule.java:114)
        at org.basex.query.func.StandardFunc.cache(StandardFunc.java:404)
        at org.basex.query.func.xquery.XQueryEval.eval(XQueryEval.java:129)
        at org.basex.query.func.xquery.XQueryEval.eval(XQueryEval.java:59)
        at org.basex.query.func.xquery.XQueryEval.iter(XQueryEval.java:44)
        at org.basex.query.expr.TypeCheck.iter(TypeCheck.java:87)
        at org.basex.query.QueryContext.iter(QueryContext.java:412)
        at org.basex.query.expr.If.iter(If.java:128)
        at org.basex.query.MainModule.iter(MainModule.java:110)
        at org.basex.query.QueryContext.iter(QueryContext.java:351)
        at org.basex.http.restxq.RestXqResponse.create(RestXqResponse.java:55)
        at org.basex.http.restxq.RestXqModule.process(RestXqModule.java:101)
        at org.basex.http.restxq.RestXqFunction.process(RestXqFunction.java:109)
        at org.basex.http.restxq.RestXqServlet.run(RestXqServlet.java:44)
        at org.basex.http.BaseXServlet.service(BaseXServlet.java:64)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)

Both '/home/chris/Downloads/xml/billing_invoice_241040.xml' and '/etc/xmlmapper/pdf_invoice.fo' exist as I use them in a local java fopfactory which processes them fine.

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