Problem: empty topics in rpc response is not tested

Closes: #841

Solution:
- merge empty topics fix
- add integration tests to verify

integration_tests/contracts/contracts/TestERC20Utility.sol

@@ -27,4 +27,9 @@ contract TestERC20Utility is ERC20 {
         _burn(msg.sender, total);
         emit __CronosSendToEthereum(recipient, amount, bridge_fee);
     }
+
+    function test_log0() public {
+        bytes32 data = "hello world";
+        log0(bytes32(data));
+    }
 }

integration_tests/test_basic.py

@@ -427,3 +427,23 @@ def test_message_call(cronos):
     assert 23828976 == receipt.cumulativeGasUsed
     assert receipt.status == 1, "shouldn't fail"
     assert len(receipt.logs) == iterations
+
+
+def test_log0(cluster):
+    """
+    test compliance of empty topics behavior
+    """
+    w3 = cluster.w3
+    contract = deploy_contract(
+        w3,
+        Path(__file__).parent
+        / "contracts/artifacts/contracts/TestERC20Utility.sol/TestERC20Utility.json",
+    )
+    tx = contract.functions.test_log0().buildTransaction({"from": ADDRS["validator"]})
+    receipt = send_transaction(w3, tx, KEYS["validator"])
+    assert len(receipt.logs) == 1
+    log = receipt.logs[0]
+    assert log.topics == []
+    assert (
+        log.data == "0x68656c6c6f20776f726c64000000000000000000000000000000000000000000"
+    )