dot/tensordot fails on 1D sparse arrays

[jakevdp]

Seems like this needs to be special-cased somewhere:

import sparse as sp
x = sp.COO.from_numpy(np.arange(10))
y = sp.COO.from_numpy(np.arange(10))
sp.dot(x, y)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-7-3dbcf0587ccb> in <module>()
      2 x = sp.COO.from_numpy(np.arange(10))
      3 y = sp.COO.from_numpy(np.arange(10))
----> 4 sp.dot(x, y)

/Users/jakevdp/github/mrocklin/sparse/sparse/core.py in dot(a, b)
    429 
    430 def dot(a, b):
--> 431     return tensordot(a, b, axes=((a.ndim - 1,), (b.ndim - 2,)))
    432 
    433 

/Users/jakevdp/github/mrocklin/sparse/sparse/core.py in tensordot(a, b, axes)
    425     res = _dot(at, bt)
    426     res = COO.from_scipy_sparse(res)  # <--- modified
--> 427     return res.reshape(olda + oldb)
    428 
    429 

/Users/jakevdp/github/mrocklin/sparse/sparse/core.py in reshape(self, shape)
    239             strides *= d
    240 
--> 241         return COO(coords, self.data, shape, has_duplicates=self.has_duplicates)
    242 
    243     def to_scipy_sparse(self):

/Users/jakevdp/github/mrocklin/sparse/sparse/core.py in __init__(self, coords, data, shape, has_duplicates)
     69         self.data = np.asarray(data)
     70         self.coords = np.asarray(coords)
---> 71         self.coords = self.coords.astype(np.min_scalar_type(max(self.shape)))
     72         assert len(data) == self.coords.shape[1]
     73         self.has_duplicates = has_duplicates

ValueError: max() arg is an empty sequence