Update missing hipscat references

src/hats/catalog/healpix_dataset/healpix_dataset.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import dataclasses
 import warnings
 from pathlib import Path
 from typing import List, Tuple, Union
@@ -153,7 +152,7 @@ def __len__(self):
             This value is undetermined when the catalog is modified, and
             therefore an error is raised.
         """
-        if self.catalog_info.total_rows is None:
+        if self.catalog_info.total_rows == 0:
             raise ValueError("The number of rows is undetermined because the catalog was modified.")
         return self.catalog_info.total_rows
 

src/hats/pixel_math/sparse_histogram.py

@@ -3,7 +3,7 @@
 import numpy as np
 from scipy.sparse import csc_array, load_npz, save_npz, sparray
 
-import hipscat.pixel_math.healpix_shim as hp
+import hats.pixel_math.healpix_shim as hp
 
 
 class SparseHistogram:

tests/hats/pixel_math/test_sparse_histogram.py

@@ -6,8 +6,8 @@
 from numpy import frombuffer
 from scipy.sparse import csr_array
 
-import hipscat.pixel_math.healpix_shim as hp
-from hipscat.pixel_math.sparse_histogram import SparseHistogram
+import hats.pixel_math.healpix_shim as hp
+from hats.pixel_math.sparse_histogram import SparseHistogram
 
 
 def test_make_empty():