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)
+            # Perform the matrix multiplication
+            result_blocks = self.blocks*other.blocks
+            # Convert scalar zeros back to ZeroMatrix objects with correct dimensions
+            from sympy.core.numbers import Zero
+            # Create a new matrix with proper ZeroMatrix objects
+            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 the block is a scalar zero, convert it to ZeroMatrix
+                    if isinstance(block, Zero):
+                        # The dimensions should be (self.rowblocksizes[i], other.colblocksizes[j])
+                        rows = self.rowblocksizes[i]
+                        cols = other.colblocksizes[j]
+                        block = ZeroMatrix(rows, cols)
+                    row.append(block)
+                new_blocks.append(row)
+            # Create the matrix using ImmutableDenseMatrix to match the expected format
+            mat = ImmutableDenseMatrix(new_blocks)
+            return BlockMatrix(mat)
         return self * other

fortitude