pd.read_html, AttributeError: AttributeError: 'NoneType' object has no attribute 'next_element'
When I try to use `pa.read_html()` to extract data from a html page, I got some error infos.
How to solve this?
Thanks.
#### Code

```
import pandas as pd
url = 'http://data.earthquake.cn/datashare/globeEarthquake_csn.html'
dfs = pd.read_html(html)
dfs
```
#### Some Infos
- `pd.__version__` : `u'0.18.1'`
- `pd.get_option('display.encoding')`: `'UTF-8'`
- webpage:  `charset=gb2312`
- Platform: Jupyter/notebook
- Python : 2.7.6
#### Error:

```
AttributeError                            Traceback (most recent call last)
<ipython-input-53-f541be1b6614> in <module>()
      1 import pandas as pd
      2 url = 'http://data.earthquake.cn/datashare/globeEarthquake_csn.html'
----> 3 dfs = pd.read_html(html)
      4 dfs

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in read_html(io, match, flavor, header, index_col, skiprows, attrs, parse_dates, tupleize_cols, thousands, encoding)
    872     _validate_header_arg(header)
    873     return _parse(flavor, io, match, header, index_col, skiprows,
--> 874                   parse_dates, tupleize_cols, thousands, attrs, encoding)

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in _parse(flavor, io, match, header, index_col, skiprows, parse_dates, tupleize_cols, thousands, attrs, encoding)
    737 
    738     ret = []
--> 739     for table in tables:
    740         try:
    741             ret.append(_data_to_frame(data=table,

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in <genexpr>((table,))
    195     def parse_tables(self):
    196         tables = self._parse_tables(self._build_doc(), self.match, self.attrs)
--> 197         return (self._build_table(table) for table in tables)
    198 
    199     def _parse_raw_data(self, rows):

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in _build_table(self, table)
    347 
    348     def _build_table(self, table):
--> 349         header = self._parse_raw_thead(table)
    350         body = self._parse_raw_tbody(table)
    351         footer = self._parse_raw_tfoot(table)

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in _parse_raw_thead(self, table)
    353 
    354     def _parse_raw_thead(self, table):
--> 355         thead = self._parse_thead(table)
    356         res = []
    357         if thead:

/usr/local/lib/python2.7/dist-packages/pandas/io/html.pyc in _parse_thead(self, table)
    411 
    412     def _parse_thead(self, table):
--> 413         return table.find_all('thead')
    414 
    415     def _parse_tbody(self, table):

/usr/local/lib/python2.7/dist-packages/bs4/element.pyc in find_all(self, name, attrs, recursive, text, limit, **kwargs)
   1257         if not recursive:
   1258             generator = self.children
-> 1259         return self._find_all(name, attrs, text, limit, generator, **kwargs)
   1260     findAll = find_all       # BS3
   1261     findChildren = find_all  # BS2

/usr/local/lib/python2.7/dist-packages/bs4/element.pyc in _find_all(self, name, attrs, text, limit, generator, **kwargs)
    527                           if isinstance(element, Tag)
    528                             and element.name == name)
--> 529                 return ResultSet(strainer, result)
    530         results = ResultSet(strainer)
    531         while True:

/usr/local/lib/python2.7/dist-packages/bs4/element.pyc in __init__(self, source, result)
   1722     that created it."""
   1723     def __init__(self, source, result=()):
-> 1724         super(ResultSet, self).__init__(result)
   1725         self.source = source

/usr/local/lib/python2.7/dist-packages/bs4/element.pyc in <genexpr>((element,))
    524             elif isinstance(name, basestring):
    525                 # Optimization to find all tags with a given name.
--> 526                 result = (element for element in generator
    527                           if isinstance(element, Tag)
    528                             and element.name == name)

/usr/local/lib/python2.7/dist-packages/bs4/element.pyc in descendants(self)
   1275         while current is not stopNode:
   1276             yield current
-> 1277             current = current.next_element
   1278 
   1279     # CSS selector code

AttributeError: 'NoneType' object has no attribute 'next_element'
```
