diff --git a/antarest/study/storage/variantstudy/business/utils.py b/antarest/study/storage/variantstudy/business/utils.py
index 6f04601ec5..933c72bed7 100644
--- a/antarest/study/storage/variantstudy/business/utils.py
+++ b/antarest/study/storage/variantstudy/business/utils.py
@@ -52,10 +52,13 @@ def get_or_create_section(json_ini: JSON, section: str) -> JSON:
 
 
 def remove_none_args(command_dto: CommandDTO) -> CommandDTO:
-    if isinstance(command_dto.args, list):
-        command_dto.args = [{k: v for k, v in args.items() if v is not None} for args in command_dto.args]
+    args = command_dto.args
+    if isinstance(args, list):
+        command_dto.args = [{k: v for k, v in args.items() if v is not None} for args in args]
+    elif isinstance(args, dict):
+        command_dto.args = {k: v for k, v in args.items() if v is not None}
     else:
-        command_dto.args = {k: v for k, v in command_dto.args.items() if v is not None}
+        raise TypeError(f"Invalid type for args: {type(args)}")
     return command_dto
 
 
diff --git a/antarest/study/storage/variantstudy/model/model.py b/antarest/study/storage/variantstudy/model/model.py
index 4b2e15e2c1..129f420481 100644
--- a/antarest/study/storage/variantstudy/model/model.py
+++ b/antarest/study/storage/variantstudy/model/model.py
@@ -1,4 +1,4 @@
-from typing import List, Optional, Tuple, Union
+import typing as t
 
 from pydantic import BaseModel
 
@@ -7,19 +7,46 @@
 
 
 class GenerationResultInfoDTO(BaseModel):
+    """
+    Result information of a snapshot generation process.
+
+    Attributes:
+        success: A boolean indicating whether the generation process was successful.
+        details: A list of tuples containing detailed information about the generation process.
+    """
+
     success: bool
-    details: List[Tuple[str, bool, str]]
+    details: t.MutableSequence[t.Tuple[str, bool, str]]
 
 
 class CommandDTO(BaseModel):
-    id: Optional[str]
+    """
+    This class represents a command.
+
+    Attributes:
+        id: The unique identifier of the command.
+        action: The action to be performed by the command.
+        args: The arguments for the command action.
+        version: The version of the command.
+    """
+
+    id: t.Optional[str]
     action: str
-    # if args is a list, this mean the command will be mapped to the list of args
-    args: Union[List[JSON], JSON]
+    args: t.Union[t.MutableSequence[JSON], JSON]
     version: int = 1
 
 
 class CommandResultDTO(BaseModel):
+    """
+    This class represents the result of a command.
+
+    Attributes:
+        study_id: The unique identifier of the study.
+        id: The unique identifier of the command.
+        success: A boolean indicating whether the command was successful.
+        message: A message detailing the result of the command.
+    """
+
     study_id: str
     id: str
     success: bool
@@ -27,7 +54,18 @@ class CommandResultDTO(BaseModel):
 
 
 class VariantTreeDTO:
-    # Don't use BaseModel as this could trigger Recursion exceptions, since we're using Pydantic with a version prior to v2.
-    def __init__(self, node: StudyMetadataDTO, children: List["VariantTreeDTO"]) -> None:
+    """
+    This class represents a variant tree structure.
+
+    Attributes:
+        node: The metadata of the study (ID, name, version, etc.).
+        children: A list of variant children.
+    """
+
+    __slots__ = ("node", "children")
+
+    def __init__(self, node: StudyMetadataDTO, children: t.MutableSequence["VariantTreeDTO"]) -> None:
+        # We are intentionally not using Pydantic’s `BaseModel` here to prevent potential
+        # `RecursionError` exceptions that can occur with Pydantic versions before v2.
         self.node = node
-        self.children = children
+        self.children = children or []