add conditional environment variables

Until now all environment variables in the kas config's
env section require a default value.
In some cases we want to rely on the weak assignment
of bitbake instead of relying on the default value of the
variable in the kas config.

This means if we assign the 'None' value or nothing to the variable
in the kas config then it is only added to BB_ENV_EXTRAWHITE or
BB_ENV_PASSTHROUGH_ADDITIONS without setting it as environment
variable.

Signed-off-by: Benedikt Niedermayr <benedikt.niedermayr@siemens.com>
[Jan: fixed overlong line]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/__version__.py

@@ -28,5 +28,5 @@ __copyright__ = 'Copyright (c) Siemens AG, 2017-2020'
 __version__ = '3.1'
 
 # Please update docs/format-changelog.rst when changing the file version.
-__file_version__ = 12
+__file_version__ = 13
 __compatible_file_version__ = 1

kas/libkas.py

@@ -275,6 +275,9 @@ def get_build_environ(build_system):
         if env_var in os.environ:
             env[env_var] = os.environ[env_var]
 
+    # filter out 'None' values
+    env = {k: v for (k, v) in env.items() if v is not None}
+
     return env
 
 

kas/schema-kas.json

@@ -94,7 +94,7 @@
         "env": {
             "type": "object",
             "additionalProperties": {
-                "type": "string"
+                "type": ["string", "null"]
             }
         },
         "target": {