Can not export an empty SFrame

[TobyRoseman]

In [1]: import turicreate as tc

In [2]: tc.SFrame().export_json('/tmp/test.json')
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-2-2449955b3c97> in <module>()
----> 1 tc.SFrame().export_json('/tmp/test.json')

/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/data_structures/sframe.pyc in export_json(self, filename, orient)
   2940         """
   2941         if orient == "records":
-> 2942             self.pack_columns(dtype=dict).export_csv(
   2943                     filename, file_header='[', file_footer=']',
   2944                     header=False, double_quote=False,

/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/data_structures/sframe.pyc in pack_columns(self, column_names, column_name_prefix, dtype, fill_na, remove_prefix, new_column_name)
   4720         with cython_context():
   4721             ret_sa = SArray(_proxy=self.__proxy__.pack_columns(column_names, dict_keys,
-> 4722                                                                dtype, fill_na))
   4723 
   4724         new_sf = self.select_columns(rest_columns)

/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/cython/cy_sframe.pyx in turicreate.cython.cy_sframe.UnitySFrameProxy.pack_columns (/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/cython/cy_sframe.cxx:10843)()
    298         return create_proxy_wrapper_from_existing_proxy(proxy)
    299 
--> 300     cpdef pack_columns(self, _column_names, _key_names, dtype, fill_na):
    301         cdef vector[string] column_names = to_vector_of_strings(_column_names)
    302         cdef vector[string] key_names = to_vector_of_strings(_key_names)

/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/cython/cy_sframe.pyx in turicreate.cython.cy_sframe.UnitySFrameProxy.pack_columns (/Users/tobyroseman/Documents/turicreate/debug/src/unity/python/turicreate/cython/cy_sframe.cxx:10695)()
    305         cdef flexible_type na_val = flexible_type_from_pyobject(fill_na)
    306         with nogil:
--> 307             proxy = self.thisptr.pack_columns(column_names, key_names, fl_type, na_val)
    308         return sarray_proxy(proxy)
    309 

RuntimeError: There is no column to pack

[dhivyaaxim]

@TobyRoseman @znation Please assign this ticket to me as I would like to try fixing it and contribute .Thanks in advance!