Trust the deserialized values

Change the (de)serialization logic, so the serialization expects that
the object is valid. All default values and validation happens now upon
deserialization. That concentrates the logic into a single place.

app/models.py

@@ -1,5 +1,6 @@
 import uuid
 
+from collections import defaultdict
 from datetime import datetime
 from flask_sqlalchemy import SQLAlchemy
 from marshmallow import Schema, fields, validate, validates, ValidationError
@@ -90,7 +91,7 @@ def from_json(cls, data):
             data.get("ansible_host"),
             data.get("account"),
             Facts.from_json(data.get("facts")),
-            data.get("system_profile", {}),
+            data.get("system_profile")
         )
 
     def to_json(self):
@@ -108,7 +109,7 @@ def to_json(self):
     def to_system_profile_json(self):
         return {
             "id": _serialize_uuid(self.id),
-            "system_profile": self.system_profile_facts or {}
+            "system_profile": self.system_profile_facts
         }
 
     def save(self):
@@ -247,13 +248,12 @@ class Facts:
 
     @classmethod
     def from_json(cls, data):
-        facts = {}
+        facts = defaultdict(lambda: {})
         for item in data or []:
             try:
-                if item["namespace"] in facts:
-                    facts[item["namespace"]].update(item["facts"])
-                else:
-                    facts[item["namespace"]] = item["facts"]
+                old_facts = facts[item["namespace"]]
+                new_facts = item["facts"] or {}
+                facts[item["namespace"]] = {**old_facts, **new_facts}
             except KeyError:
                 # The facts from the request are formatted incorrectly
                 raise InputFormatException("Invalid format of Fact object.  Fact "
@@ -263,7 +263,7 @@ def from_json(cls, data):
     @classmethod
     def to_json(cls, facts):
         return [
-            {"namespace": namespace, "facts": facts or {}}
+            {"namespace": namespace, "facts": facts}
             for namespace, facts in facts.items()
         ]