Invocable initialization should not remove config values that are emp…

…ty strings (#593)

src/steamship/invocable/invocable.py

@@ -180,7 +180,7 @@ def __init__(
         # creation. All subsequent method invocations reuse that frozen config.
         config = {
             **secret_kwargs,
-            **{k: v for k, v in (config or {}).items() if v != ""},
+            **{k: v for k, v in (config or {}).items()},
         }
 
         # Finally, we set the config object to an instance of the class returned by `self.config_cls`