Update ownable check to validate zero address

src/openzeppelin/access/ownable.cairo

@@ -49,6 +49,7 @@ namespace Ownable:
         let (owner) = Ownable.owner()
         let (caller) = get_caller_address()
         with_attr error_message("Ownable: caller is not the owner"):
+            assert_not_zero(caller)
             assert owner = caller
         end
         return ()

tests/access/test_Ownable.py

@@ -5,7 +5,8 @@
     ZERO_ADDRESS,
     assert_event_emitted,
     get_contract_class,
-    cached_contract
+    cached_contract,
+    assert_revert
 )
 
 
@@ -85,6 +86,12 @@ async def test_renounceOwnership(ownable_factory):
     executed_info = await ownable.owner().call()
     assert executed_info.result == (ZERO_ADDRESS,)
 
+    # Protected function cannot be called from zero address
+    await assert_revert(
+        ownable.protected_function().call(),
+        reverted_with="Ownable: caller is not the owner"
+    )
+
 
 @pytest.mark.asyncio
 async def test_renounceOwnership_emits_event(ownable_factory):

tests/mocks/Ownable.cairo

@@ -5,6 +5,7 @@
 from starkware.cairo.common.cairo_builtins import HashBuiltin
 from starkware.starknet.common.syscalls import get_caller_address
 from openzeppelin.access.ownable import Ownable
+from starkware.cairo.common.bool import TRUE
 
 @constructor
 func constructor{
@@ -45,3 +46,13 @@ func renounceOwnership{
     Ownable.renounce_ownership()
     return ()
 end
+
+@external
+func protected_function{
+        syscall_ptr : felt*,
+        pedersen_ptr : HashBuiltin*,
+        range_check_ptr
+    }() -> (res: felt):
+    Ownable.assert_only_owner()
+    return (TRUE)
+end