Finished

Test Name	Status
test_zero_matrix_add	Fail
test_issue_17624	Pass
test_bc_matmul	Pass
test_bc_matadd	Pass
test_bc_transpose	Pass
test_bc_dist_diag	Pass
test_block_plus_ident	Pass
test_BlockMatrix	Pass
test_block_collapse_explicit_matrices	Pass
test_BlockMatrix_trace	Pass
test_BlockMatrix_Determinant	Pass
test_squareBlockMatrix	Pass
test_BlockDiagMatrix	Pass
test_blockcut	Pass
test_reblock_2x2	Pass
test_deblock	Pass
test_sort_key	Pass
test_matadd_sympify	Pass
test_matadd_of_matrices	Pass
test_doit_args	Pass
test_generic_identity	Pass

     def _blockmul(self, other):
         if (isinstance(other, BlockMatrix) and
                 self.colblocksizes == other.rowblocksizes):
+            return BlockMatrix(self.blocks*other.blocks)
+            from sympy.core.numbers import Zero
+            result_blocks = self.blocks*other.blocks
+            # Convert Zero objects back to ZeroMatrix with proper dimensions
+            if result_blocks.has(Zero):
+                from sympy.matrices.immutable import ImmutableDenseMatrix
+                new_blocks = []
+                for i in range(result_blocks.shape[0]):
+                    row = []
+                    for j in range(result_blocks.shape[1]):
+                        block = result_blocks[i, j]
+                        if isinstance(block, Zero):
+                            # Zero matrix should have proper dimensions
+                            block = ZeroMatrix
+                            rows = self.blocks[i, 0].rows
+                            cols = other.blocks[0, j].cols
+                            row.append(ZeroMatrix(rows, cols))
+                        else:
+                            row.append(block)
+                    new_blocks.append(row)
+                result_blocks = ImmutableDenseMatrix(new_blocks)
+            return BlockMatrix(result_blocks)
         return self * other

great