XStream ConversionException the second time I parse an XML file

[Tekime]

I'm trying to read a TreeMap from an XML file using XStream (I previously created the XML file using XStream too) in my Android application.I simply do this in a static method of a class\[code\]File f = new File(Environment.getExternalStorageDirectory(), "map.xml");XStream xStream = new XStream(new DomDriver());@SuppressWarnings("unchecked") TreeMap<String,Object> map = (TreeMap<String,Object>) xStream.fromXML(f);\[/code\]and then I use the values from the TreeMap with no problems... the first time.The thing is, if I invoke the method for a second time, it doesn't matter if I do it just after the first execution or after a while, I get this: \[code\]05-24 08:33:53.404: E/AndroidRuntime(15543): FATAL EXCEPTION: main05-24 08:33:53.404: E/AndroidRuntime(15543): com.thoughtworks.xstream.converters.ConversionException: null : null05-24 08:33:53.404: E/AndroidRuntime(15543): ---- Debugging information ----05-24 08:33:53.404: E/AndroidRuntime(15543): cause-exception : java.lang.NullPointerException05-24 08:33:53.404: E/AndroidRuntime(15543): cause-message : null05-24 08:33:53.404: E/AndroidRuntime(15543): class : java.util.TreeMap05-24 08:33:53.404: E/AndroidRuntime(15543): required-type : java.util.TreeMap05-24 08:33:53.404: E/AndroidRuntime(15543): converter-type : com.thoughtworks.xstream.converters.collections.TreeMapConverter05-24 08:33:53.404: E/AndroidRuntime(15543): path : /tree-map05-24 08:33:53.404: E/AndroidRuntime(15543): version : 0.005-24 08:33:53.404: E/AndroidRuntime(15543): -------------------------------05-24 08:33:53.404: E/AndroidRuntime(15543): at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:79)05-24 08:33:53.404: E/AndroidRuntime(15543): at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:65)[...]05-24 08:33:53.404: E/AndroidRuntime(15543): Caused by: java.lang.NullPointerException05-24 08:33:53.404: E/AndroidRuntime(15543): at java.util.TreeMap.find(TreeMap.java:277)05-24 08:33:53.404: E/AndroidRuntime(15543): at java.util.TreeMap.putInternal(TreeMap.java:240)05-24 08:33:53.404: E/AndroidRuntime(15543): at java.util.TreeMap.put(TreeMap.java:186)05-24 08:33:53.404: E/AndroidRuntime(15543): at java.util.AbstractMap.putAll(AbstractMap.java:381)05-24 08:33:53.404: E/AndroidRuntime(15543): at com.thoughtworks.xstream.converters.collections.TreeMapConverter.populateTreeMap(TreeMapConverter.java:150)[...]\[/code\]with the same file. In fact, if I try to read the file and then pass it to XStream as a String, I get the same exception (but the XML String is created OK).Does anyone know what the cause could be or has experienced the same problem and know how to fix it?Thanks!