fix: handle empty description string in class generator (#2677)

When API schema has description: "" (empty string), dict.get()
returns the empty string instead of falling back to
MISSING_DESCRIPTION_STR, causing empty class docstrings.

Use 'or' instead of get() default to handle both missing and
empty/falsy description values.

Author: rnetser

class_generator/parsers/explain_parser.py

@@ -89,7 +89,7 @@ def parse_explain(kind: str) -> list[dict[str, Any]]:
 
         resource_dict: dict[str, Any] = {
             "base_class": "NamespacedResource" if namespaced else "Resource",
-            "description": _kind_schema.get("description", MISSING_DESCRIPTION_STR),
+            "description": _kind_schema.get("description") or MISSING_DESCRIPTION_STR,
             "fields": [],
             "spec": [],
         }