Error: lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1

[mansi-aggarwal-2504]

On line 157, in create_pascal_tf_record.py (from extra folder), when I run xml_str = fid.read(), the resultant xml_str is empty. And hence, when I run xml = etree.fromstring(xml_str), it's throwing the following error:

    xml = etree.fromstring(xml_str)
  File "src/lxml/etree.pyx", line 3237, in lxml.etree.fromstring
  File "src/lxml/parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
  File "src/lxml/parser.pxi", line 1777, in lxml.etree._parseDoc
  File "src/lxml/parser.pxi", line 1082, in lxml.etree._BaseParser._parseUnicodeDoc
  File "src/lxml/parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
  File "src/lxml/parser.pxi", line 725, in lxml.etree._handleParseResult
  File "src/lxml/parser.pxi", line 654, in lxml.etree._raiseParseError
  File "<string>", line 1
lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1

I am using the VOC 2012 data and I check the first image and its xml in labelimg and it's not empty.
So why am I getting this error?