Fix processing boot values

If a bool variable is False, some interpolation steps were
not printed

Change-Id: I8665bbe10e0f72b721aa86290894371d8ac0233d
diff --git a/reclass_tools/reclass_models.py b/reclass_tools/reclass_models.py
index 37f0bb6..238caf3 100644
--- a/reclass_tools/reclass_models.py
+++ b/reclass_tools/reclass_models.py
@@ -91,7 +91,7 @@
         if self.track_key_path:
             key = helpers.get_nested_key(entity.parameters.as_dict(),
                                          path=self.track_key_path)
-            if key:
+            if key is not None:
                 print("# " + ' < '.join(seen['__visited']))
                 out_dict = {}
                 helpers.create_nested_key(out_dict, ['parameters'] + self.track_key_path, key)
@@ -114,7 +114,7 @@
         if self.track_key_path:
             key = helpers.get_nested_key(result.parameters.as_dict(),
                                          path=self.track_key_path)
-            if key:
+            if key is not None:
                 print("### Final result after interpolation: ###")
                 out_dict = {}
                 helpers.create_nested_key(out_dict, ['parameters'] + self.track_key_path, key)