Add is_list property to _YamlDefaultValue class

Currently moulin crashes when it tries to check if the default value
is a list. Add support for storing lists to the _YamlDefaultValue.

Signed-off-by: Mykyta Poturai <[email protected]>

moulin/yaml_wrapper.py

@@ -18,10 +18,10 @@
 class _YamlDefaultValue:
     """
     Helper class that have the same API as YamlValue, but is
-    constructed from a primitive type. It is used to provide default
+    constructed from a builtin type. It is used to provide default
     value in YamlValue.get() method
     """
-    def __init__(self, val: Union[bool, str, int, float, None]):
+    def __init__(self, val: Union[bool, str, int, float, List, None]):
         self._val = val
 
     def __bool__(self):
@@ -55,6 +55,11 @@ def as_float(self) -> float:
             raise TypeError("Expected float value")
         return self._val
 
+    @property
+    def is_list(self) -> bool:
+        """Check if this node represents a list"""
+        return isinstance(self._val, list)
+
 
 class YamlValue:  # pylint: disable=too-few-public-methods
     """Wrapper for yaml.Node class. It provides type-safe access to YAML nodes"""