snap.py: fix snap.get optional key (canonical#125)

Fix snap.get method to handle the case where the key is falsy. Treat it
as no key provided, which results in the expected behavior to get all
values from snap configs.

lib/charms/operator_libs_linux/v2/snap.py

@@ -83,7 +83,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 6
+LIBPATCH = 7
 
 
 # Regex to locate 7-bit C1 ANSI sequences
@@ -319,7 +319,10 @@ def get(self, key: Optional[str], *, typed: bool = False) -> Any:
                 Default is to return a string.
         """
         if typed:
-            config = json.loads(self._snap("get", ["-d", key]))
+            args = ["-d"]
+            if key:
+                args.append(key)
+            config = json.loads(self._snap("get", args))
             if key:
                 return config.get(key)
             return config

tests/integration/test_snap.py

@@ -116,6 +116,22 @@ def test_snap_set_and_get_with_typed():
 
     assert lxd.get("criu.enable", typed=True) == "true"
     assert lxd.get("ceph.external", typed=True) == "false"
+    assert lxd.get(None, typed=True) == {
+        "true": True,
+        "false": False,
+        "integer": 1,
+        "float": 2.0,
+        "list": [1, 2.0, True, False, None],
+        "dict": {
+            "true": True,
+            "false": False,
+            "integer": 1,
+            "float": 2.0,
+            "list": [1, 2.0, True, False, None],
+        },
+        "criu": {"enable": "true"},
+        "ceph": {"external": "false"},
+    }
 
 
 def test_snap_set_and_get_untyped():