NPE when importing some TMX file

$ tmpotter
[AWT-EventQueue-0] INFO org.tmpotter.util.TmxReader2 - フィアル読み込み中...: /home/miurahr/tmpotter/export.tmx
[AWT-EventQueue-0] INFO org.tmpotter.util.TmxReader2 - TMXファイル作成ツール名 TMPotter
[AWT-EventQueue-0] INFO org.tmpotter.util.TmxReader2 - TMXファイル作成ツールバージョン 0.8_3_
[AWT-EventQueue-0] INFO org.tmpotter.util.TmxReader2 - TMXファイルの分割タイプ sentence
[AWT-EventQueue-0] INFO org.tmpotter.util.TmxReader2 - TMXファイルのソース言語 EN
[AWT-EventQueue-0] INFO org.tmpotter.filters.FilterManager - Filter error
java.lang.NullPointerException
    at java.lang.String.regionMatches(String.java:1348)
    at org.tmpotter.util.TmxReader2.getTuvByLang(TmxReader2.java:657)
    at org.tmpotter.util.TmxReader2.readTmx(TmxReader2.java:177)
    at org.tmpotter.filters.tmx.TmxFilter.parseFile(TmxFilter.java:167)
    at org.tmpotter.filters.tmx.TmxFilter.parseFile(TmxFilter.java:184)
    at org.tmpotter.filters.FilterManager.loadFile(FilterManager.java:113)
    at org.tmpotter.ui.ActionHandler.doImport(ActionHandler.java:121)
    at org.tmpotter.ui.ActionHandler.onNewImport(ActionHandler.java:536)
    at org.tmpotter.ui.ActionHandler.buttonNewActionPerformed(ActionHandler.java:632)

Source TMX file is such as

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE tmx SYSTEM "tmx14.dtd">
<tmx version="1.4">
  <header creationtool="TMPotter" o-tmf="tmpotter TMX" adminlang="EN-US" datatype="plaintext" creationtoolversion="0.8_3_" segtype="sentence" srclang="EN">
</header>
  <body>
    <tu>
      <tuv xml:lang="EN">
        <seg>Writing your first patch for Django</seg>
      </tuv>
      <tuv xml:lang="JA">
        <seg>Writing your first patch for Django</seg>
      </tuv>
    </tu>
    <tu>
      <tuv xml:lang="EN">
        <seg>Introduction</seg>
      </tuv>
      <tuv xml:lang="JA">
        <seg>Introduction</seg>
      </tuv>
    </tu>

miurahr / tmpotter

NPE when importing some TMX file #53