text: Title: Error in reading data into a dataframe on encountering an empty cell
  Body: I have the following data in an xl sheet, cell A7 onwards
  
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  <head>
  
  <meta name=ProgId content=Excel.Sheet>
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  <body link="#0563C1" vlink="#954F72">
  
  
  
    | FY-5 |   | FY-4 | FY-3 | FY-2 | FY-1 | FY0
  -- | -- | -- | -- | -- | -- | -- | --
  INE002A01018 | 64852 | NULL | 85490 | 89193 | 80298 | 120991 | 142908
  INE467B01029 | 32532 | NULL | 39512 | 42110 | 46547 | 53048 | 59259
  INE982J01020 | NULL | NULL | -4343.8 | -2634.2 | -1763.4 | -2332.4 | -1631.5
  
  
  
  </body>
  
  </html>
  
  I am reading this into a pandas dataframe using the following:
  ```
  df = sheet.range('A7').options(pd.DataFrame, 
                                       header=1,
                                       index=False, 
                                       empty = "NA",
                                       expand='table').value
  df
  
  ```
  Output is:
  <html>
  <body>
  <!--StartFragment-->
  
  NA | FY-5
  -- | --
  INE002A01018 | 64852.0
  INE467B01029 | 32532.0
  INE982J01020 | NULL
  
  <!--EndFragment-->
  </body>
  </html>
  
  Basically, it stops reading the table on encountering an empty cell (C7). Setting the attribute "empty" to "NA" does not solve the problem. I cannot use the "used_range" attribute because this is just 1 table of many in the sheet.
  
  Any ideas on what I can do to read the whole table correctly?
  
  Thanks!
  