[validator] Fix no valid address on instantiation of Validator

* bump version

pyhmy/_version.py

@@ -7,5 +7,5 @@ Provides pyhmy version information.
 
 from incremental import Version
 
-__version__ = Version('pyhmy', 20, 5, 7)
+__version__ = Version('pyhmy', 20, 5, 8)
 __all__ = ["__version__"]

pyhmy/validator.py

@@ -44,6 +44,8 @@ class Validator:
     min_required_delegation = 10000
 
     def __init__(self, address):
+        if not isinstance(address, str):
+            raise InvalidValidatorError(1, f'given ONE address was not a string.')
         if not is_valid_address(address):
             raise InvalidValidatorError(1, f'{address} is not valid ONE address')
         self._address = address