I am getting the IIOMetadata  customer  from the JPEG Reader by calling Reader.getImageMetadata(0). From this metadata  customer  I am getting the Node  customer  by calling IIOMetadata.getAsTree() and passing the native metadata format. I called IIOMetadata.mergeTree() and passed the native format name and the Node  customer  obtained from the getAsTree() method. Typically I am merging the same tree with the same metadata  customer . In this case, mergeTree() is throwing a NPE (for JPEG) which is given below:

java.lang.NullPointerException
at com.sun.imageio.plugins.jpeg.MarkerSegment.getAttributeValue(MarkerSegment.java:131)
at com.sun.imageio.plugins.jpeg.JPEGMetadata.mergeDHTNode(JPEGMetadata.java:1254)
at com.sun.imageio.plugins.jpeg.JPEGMetadata.mergeSequenceSubtree(JPEGMetadata.java:1127)
at com.sun.imageio.plugins.jpeg.JPEGMetadata.mergeNativeTree(JPEGMetadata.java:1092)
at com.sun.imageio.plugins.jpeg.JPEGMetadata.mergeTree(JPEGMetadata.java:1064)
at ReaderImageMetadataTest.<init>(ReaderImageMetadataTest.java:59)
at ReaderImageMetadataTest.main(ReaderImageMetadataTest.java:115)

If mergeTree() does not support merging the same node obtained from getAsTree() it must throw a meaningful exception or IIOInvalidTreeException as specified by the specification. NullPointerExceptions leaves the user clueless on why it is being thrown.

This is reproducible on all platforms right from JDK1.4+.

I have attached a sample code. Execute the sample code as follows. 
java ReaderImageMetadataTest <img file>
You will get the above exception in the console.

N/A

 The problem here is quite trivial, it could be an mistype at line 1253:
 we get attribute list form parent node instead of child node.
 The list of parent attributes does not contain attributes related to the
 child node and this fact causes the NPE in the  method
 MarkerSegment.getAttributeValue() when we try to get child related
 attribute.

 The solution is to get attribute list form child node.

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