Reject str as a primitive in to_hex()

Adds an exception in `to_hex()` if str
type is provided to primitive argument

Relates to #85

eth_utils/conversions.py

@@ -39,7 +39,10 @@ def to_hex(primitive=None, hexstr=None, text=None):
     if isinstance(primitive, (bytes, bytearray)):
         return encode_hex(primitive)
     elif is_string(primitive):
-        return to_hex(text=primitive)
+        raise TypeError(
+            "Unsupported type: The primitive argument must be one of: bytes,"
+            "bytearray, int or bool and not str"
+        )
 
     if is_integer(primitive):
         return hex(primitive)

tests/conversion-utils/test_conversions.py

@@ -212,3 +212,8 @@ def test_to_hex_text(val, expected):
 )
 def test_to_hex_cleanup_only(val, expected):
     assert to_hex(hexstr=val) == expected
+
+
+def test_to_hex_exception():
+    with pytest.raises(TypeError, match="Unsupported type: The primitive argument"):
+        to_hex(primitive='string')