Fix failing test and add new test file

src/main/java/net/sf/jabref/logic/msbib/MSBibConverter.java

@@ -11,9 +11,11 @@
 import net.sf.jabref.model.entry.FieldName;
 
 public class MSBibConverter {
+
     private static final String MSBIB_PREFIX = "msbib-";
     private static final String BIBTEX_PREFIX = "BIBTEX_";
 
+
     public static MSBibEntry convert(BibEntry entry) {
         MSBibEntry result = new MSBibEntry();
 
@@ -55,7 +57,7 @@ public static MSBibEntry convert(BibEntry entry) {
         }
 
         if (!entry.getFieldOptional(FieldName.YEAR).isPresent()) {
-            result.year = entry.getFieldOrAlias(FieldName.YEAR).orElse("");
+            result.year = entry.getFieldOrAlias(FieldName.YEAR).orElse(null);
         }
 
         // Value must be converted

src/test/resources/net/sf/jabref/logic/exporter/MsBibExportFormatTest7.bib

@@ -0,0 +1,15 @@
+% Encoding: UTF-8
+
+@InBook{Orlowski;2011,
+  author        = {Adam Czarnecki; Cezary Or{\l}owski;},
+  title         = {Application of Ontology In the ITIL Domain},
+  date          = {2011-03-12},
+  publisher     = {Oficyna Wydawnicza Politechniki Wrocławskiej},
+  pages         = {99--108},
+  doi           = {10.13140/2.1.3259.2169},
+  __markedentry = {[Christoph Schwentker:6]},
+  journaltitle  = {Information Systems Architecture and Technology: Service Oriented Networked Systems},
+  timestamp     = {2016.08.17},
+}
+
+@Comment{jabref-meta: databaseType:biblatex;}

src/test/resources/net/sf/jabref/logic/exporter/MsBibExportFormatTest7.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<b:Sources xmlns:b="http://schemas.openxmlformats.org/officeDocument/2006/bibliography" xmlns="http://schemas.openxmlformats.org/officeDocument/2006/bibliography" SelectedStyle="">
+<b:Source>
+<b:BIBTEX_Entry>inbook</b:BIBTEX_Entry>
+<b:SourceType>BookSection</b:SourceType>
+<b:Title>Application of Ontology In the ITIL Domain</b:Title>
+<b:Tag>Orlowski;2011</b:Tag>
+<b:Publisher>Oficyna Wydawnicza Politechniki Wrocławskiej</b:Publisher>
+<b:DOI>10.13140/2.1.3259.2169</b:DOI>
+<b:Author>
+<b:Author>
+<b:NameList>
+<b:Person>
+<b:Last>Czarnecki</b:Last>
+<b:Middle>and Or{\l}owski, Cezary</b:Middle>
+<b:First>Adam</b:First>
+</b:Person>
+</b:NameList>
+</b:Author>
+</b:Author>
+<b:Pages>99-108</b:Pages>
+<b:Year>2011</b:Year>
+<b:StandardNumber> DOI: 10.13140/2.1.3259.2169</b:StandardNumber>
+</b:Source>
+</b:Sources>