fix: allow required fields list to be specified as empty

Refs: #651

Author: benweint

openapi_python_client/schema/openapi_schema_pydantic/schema.py

@@ -34,7 +34,7 @@ class Schema(BaseModel):
     uniqueItems: Optional[bool] = None
     maxProperties: Optional[int] = Field(default=None, ge=0)
     minProperties: Optional[int] = Field(default=None, ge=0)
-    required: Optional[List[str]] = Field(default=None, min_length=1)
+    required: Optional[List[str]] = Field(default=None)
     enum: Union[None, List[Any]] = Field(default=None, min_length=1)
     const: Union[None, StrictStr, StrictInt, StrictFloat, StrictBool] = None
     type: Union[DataType, List[DataType], None] = Field(default=None)