[configModel] Create path when it is partial (RedHatProductSecurity#150)

This kind of YAML was causing trouble:

```yaml
a:
```

When reading this, it is converted to `{"a": None}`, but configModel
would refuse to go down that path to set a value (unless we overwrite).

This change fixes that: in this condition, config.set() no longer
consider setting `a.b` as overwriting `None` to a dictionary

This fixes the ZAP template configuration, where the following happened:

```yaml
general:
  container:
```

the code would refuse to set `container.parameters.executable` because
container existed but points to `None`

This resulted in `zap.sh` not being set

configmodel/__init__.py

@@ -116,7 +116,11 @@ def set(self, path, value, overwrite=True):
                 walk = walk[key]
                 continue
             tmp = walk[key]
-            # case 2: not a "dictionary" type: warn and overwrite (if True)
+            # case 2: the value is None (path partially exists): initialize a dictionary
+            if tmp is None:
+                walk[key] = {}
+                tmp = walk[key]
+            # case 3: not a "dictionary" type: warn and overwrite (if True)
             if not isinstance(tmp, dict):
                 logging.warning(
                     f"RapidastConfigModel.set: Incompatible {path} at {tmp}"

tests/configmodel/test_configmodel.py

@@ -27,6 +27,7 @@ def generate_some_nested_config():
         "key4": "value4",
         "nested": {"morenested": {"key3": "nestedvalue"}},
         "nothing": None,
+        "falsekey": False,
     }
 
 
@@ -87,6 +88,18 @@ def test_configmodel_set(some_nested_config):
     myconf.set("nested.morenested", "mynewval", overwrite=True)
     assert myconf.get("nested.morenested") == "mynewval"
 
+    # deep sets
+    # `set` should rewrite a `None` value even on `overwrite=False`
+    myconf.set("nothing.some.more.nested", "newval", overwrite=False)
+    assert myconf.get("nothing.some.more.nested") == "newval"
+    # but should not rewrite a value set to False value
+    myconf.set("falsekey.some.more.nested", "newval", overwrite=False)
+    assert not myconf.exists("falsekey.some.more.nested")
+    # unless we overwrite
+    myconf.set("falsekey.some.more.nested", "newval", overwrite=True)
+    assert myconf.exists("falsekey.some.more.nested")
+    assert myconf.get("falsekey.some.more.nested") == "newval"
+
 
 def test_configmodel_move(some_nested_config):
     myconf = RapidastConfigModel(some_nested_config)