#data
<gpx><metadata>
  <copyright>
  </copyright>
</metadata></gpx>
#parsed
{"license":{}}

#data
<gpx><metadata>
  <copyright author="">
  </copyright>
</metadata></gpx>
#parsed
{"license":{}}

#data
<gpx><metadata>
  <copyright author="hoge">
  </copyright>
</metadata></gpx>
#parsed
{"license":{"holder":"hoge"}}

#data
<gpx><metadata>
  <copyright>
    <year>1245</year>
  </copyright>
</metadata></gpx>
#parsed
{"license":{"year":1245}}

#data
<gpx><metadata>
  <copyright>
    <year>31</year>
  </copyright>
</metadata></gpx>
#parsed
{"license":{}}

#data
<gpx><metadata>
  <copyright>
    <year>10000</year>
  </copyright>
</metadata></gpx>
#parsed
{"license":{"year":10000}}

#data
<gpx><metadata>
  <copyright>
    <license>https://foo</license>
  </copyright>
</metadata></gpx>
#parsed
{"license":{"url":"https://foo/"}}