When properties is null, java.lang.ClassCastException is generated. This fixes the issue #14
java.lang.ClassCastException: javax.json.JsonValueImpl cannot be cast to javax.json.JsonObject
at org.glassfish.json.JsonObjectBuilderImpl$JsonObjectImpl.getJsonObject(JsonObjectBuilderImpl.java:242)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.getTags(GeoJsonReader.java:228)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.fillTagsFromFeature(GeoJsonReader.java:217)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parseLineString(GeoJsonReader.java:145)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parseGeometry(GeoJsonReader.java:107)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parseFeature(GeoJsonReader.java:88)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parseFeatureCollection(GeoJsonReader.java:81)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parseRoot(GeoJsonReader.java:64)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.parse(GeoJsonReader.java:55)
at org.openstreetmap.josm.plugins.geojson.GeoJsonReader.doParseDataSet(GeoJsonReader.java:240)
at org.openstreetmap.josm.plugins.geojson.GeoJsonFileImporter.importData(GeoJsonFileImporter.java:50)
at org.openstreetmap.josm.gui.io.importexport.FileImporter.importDataHandleExceptions(FileImporter.java:95)
at org.openstreetmap.josm.actions.OpenFileAction$OpenFileTask.importData(OpenFileAction.java:366)
at org.openstreetmap.josm.actions.OpenFileAction$OpenFileTask.realRun(OpenFileAction.java:319)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.doRealRun(PleaseWaitRunnable.java:95)
at org.openstreetmap.josm.gui.PleaseWaitRunnable.run(PleaseWaitRunnable.java:143)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
When properties is null, java.lang.ClassCastException is generated. This fixes the issue #14