code: public ByteBuffer getByteBuffer(String attrName) {
          Object val = attributes.get(attrName);
          return toByteBuffer(val);
      }
docs: Returns the value of the specified attribute in the current item as a
  <code>ByteBuffer</code>; or null if the attribute either doesn't exist or
  the attribute value is null.
  
  @throws IncompatibleTypeException
  if the attribute value cannot be converted into a byte array
  
  @see #isNull(String) #isNull(String) to check if the attribute value is
  null.
  @see #isPresent(String) #isPresent(String) to check if the attribute
  value is present.