fix: must either be empty or all are sparse

Author: hexgnu

pandas/core/dtypes/concat.py

@@ -89,10 +89,10 @@ def _get_series_result_type(result, objs=None):
 def _get_frame_result_type(result, objs):
     """
     return appropriate class of DataFrame-like concat
-    if any block is SparseBlock, return SparseDataFrame
+    if all blocks are SparseBlock, return SparseDataFrame
     otherwise, return 1st obj
     """
-    if all(b.is_sparse for b in result.blocks):
+    if result.blocks and all(b.is_sparse for b in result.blocks):
         from pandas.core.sparse.api import SparseDataFrame
         return SparseDataFrame
     else: