diff --git a/adala/skills/collection/prompt_improvement.py b/adala/skills/collection/prompt_improvement.py
index 3bd632b9..84d71b65 100644
--- a/adala/skills/collection/prompt_improvement.py
+++ b/adala/skills/collection/prompt_improvement.py
@@ -9,7 +9,8 @@
     AfterValidator,
 )
 from adala.skills import Skill
-from typing import Any, Dict, List, Optional, Union, Type
+from typing import Any, Dict, List, Optional, Type, Union
+
 from typing_extensions import Annotated
 from adala.skills import AnalysisSkill
 from adala.utils.parse import parse_template
diff --git a/adala/utils/pydantic_generator.py b/adala/utils/pydantic_generator.py
index 52c43e67..ad19b264 100644
--- a/adala/utils/pydantic_generator.py
+++ b/adala/utils/pydantic_generator.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, List, Optional, Type, Union, Tuple, Literal, Set
+from typing import Any, Dict, List, Optional, Type, Union, Tuple, Literal, Set, get_origin, get_args
 from enum import Enum
 from datetime import datetime
 from pydantic import BaseModel, Field, create_model
@@ -95,8 +95,12 @@ def json_schema_to_pydantic_field(json_schema: Dict[str, Any]) -> Tuple[Any, Fie
         if constraint in json_schema:
             field_params[constraint] = json_schema[constraint]
 
+    # Use None default for Optional types so they aren't required
+    is_optional = get_origin(type_) is Union and type(None) in get_args(type_)
+    default = None if is_optional else ...
+
     # Create a Field object with the type and optional parameters.
-    return type_, Field(..., **field_params)
+    return type_, Field(default, **field_params)
 
 
 def json_schema_to_pydantic_type(
@@ -115,6 +119,13 @@ def json_schema_to_pydantic_type(
 
     type_ = json_schema.get("type")
 
+    # Handle union types: ["string", "null"] → Optional[str]
+    if isinstance(type_, list):
+        non_null = [t for t in type_ if t != 'null']
+        has_null = len(non_null) < len(type_)
+        inner = json_schema_to_pydantic_type({**json_schema, 'type': non_null[0]})
+        return Optional[inner] if has_null else inner
+
     if type_ == "string":
         if "format" in json_schema:
             format_ = json_schema["format"]
diff --git a/pyproject.toml b/pyproject.toml
index 11e1e7d3..5193305a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -46,7 +46,12 @@ dependencies = [
     "pandarallel (>=1.6.5,<2.0.0)",
     "instructor (>=1.14.5, <2.0.0)",
     "async-lru (>=2.0.5,<3.0.0)",
-    "jinja2 (>=3.1.6,<4.0)"
+    "jinja2 (>=3.1.6,<4.0)",
+    "lxml>=6.0.2",
+    "appdirs>=1.4.4",
+    "xmljson>=0.2.1",
+    "jsf>=0.11.2",
+    "datamodel-code-generator>=0.54.1"
 ]
 
 [project.urls]