Role library now requires non-zero addresses. (#1303)

* The role library now requires non-zero addresses.

* Fixed SignatureBouncer checks with null address.

* change ternary operator for or operator

* adapt to new variable name convention

* Update Roles.sol

contracts/drafts/SignatureBouncer.sol

@@ -132,6 +132,7 @@ contract SignatureBouncer is SignerRole {
     address signer = hash
       .toEthSignedMessageHash()
       .recover(signature);
-    return isSigner(signer);
+
+    return signer != address(0) && isSigner(signer);
   }
 }