[Definitions][Fixed] Empty definition handling

Avoid interpreting them as the "None" string, now they are just None

See #757

CHANGELOG.md

@@ -72,6 +72,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - A mechanism to paste images from outputs (#714)
 
 ### Fixed
+- Definitions: avoid interpreting empty definitions as the "None" string
+  (See #757)
 - Guess for 3rd party dir: not just for v6
 - SubParts filter:
   - iBoM and Schematic print didn't take it into account (#716)

docs/source/Changelog.rst

@@ -111,6 +111,8 @@ Added
 Fixed
 ~~~~~
 
+-  Definitions: avoid interpreting empty definitions as the “None”
+   string (See #757)
 -  Guess for 3rd party dir: not just for v6
 -  SubParts filter:
 

kibot/config_reader.py

@@ -77,6 +77,9 @@ def update_dict(d, u):
 def do_replace(k, v, content, replaced):
     key = '@'+k+'@'
     if key in content:
+        # Handle empty definitions keeping YAML's "null"
+        if v is None:
+            v = 'null'
         logger.debugl(2, '- Replacing {} -> {}'.format(key, v))
         content = content.replace(key, str(v))
         replaced = True