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)
+            # Multiply the blocks
+            result_blocks = self.blocks * other.blocks
+            # Convert Zero objects back to ZeroMatrix with appropriate dimensions
+            from sympy import S
+            from sympy.matrices.immutable import ImmutableDenseMatrix
+            # Create a new matrix with converted elements
+            new_blocks = [[None for _ in range(result_blocks.cols)] for _ in range(result_blocks.rows)]
+            for i in range(result_blocks.rows):
+                for j in range(result_blocks.cols):
+                    element = result_blocks[i, j]
+                    if element == S.Zero:
+                        # Determine the dimensions based on block structure
+                        # Row dimension comes from self's rowblocksizes[i]
+                        # Col dimension comes from other's colblocksizes[j]
+                        rows = self.rowblocksizes[i]
+                        cols = other.colblocksizes[j]
+                        new_blocks[i][j] = ZeroMatrix(rows, cols)
+                    else:
+                        new_blocks[i][j] = element
+            result_blocks = ImmutableDenseMatrix(new_blocks)
+            return BlockMatrix(result_blocks)
         return self * other

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