bug: RailsConfig throws error when adding configs

[JashG]

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Python version (python --version)

Python 3.10.2

Operating system/version

MacOS 15.5

NeMo-Guardrails version (if you must use a specific version and not the latest

0.15.0

Describe the bug

The RailsConfig class allows for adding two config objects. I encountered two cases where this function throws an error:

1. prompts is None for at least one RailsConfig object:

config1 = RailsConfig(
  models=[
    Model(type="main", engine="openai", model="gpt-3.5-turbo")
  ],
)
config2 = RailsConfig(
  models=[
    Model(type="secondary", engine="anthropic", model="claude-3")
  ],
)

combined_config = config1 + config2

Error:

    @root_validator(pre=True, allow_reuse=True)
    def check_output_parser_exists(cls, values):
        tasks_requiring_output_parser = [
            "self_check_input",
            "self_check_facts",
            "self_check_output",
            # "content_safety_check input $model",
            # "content_safety_check output $model",
        ]
        prompts = values.get("prompts", [])
>       for prompt in prompts:
E       TypeError: 'NoneType' object is not iterable

nemoguardrails/rails/llm/config.py:1414: TypeError: 'NoneType' object is not iterable

2. config_path is None for at least one RailsConfig object:

config1 = RailsConfig(
  models=[
    Model(type="main", engine="openai", model="gpt-3.5-turbo")
  ],
  prompts=[]
)
config2 = RailsConfig(
  models=[
    Model(type="secondary", engine="anthropic", model="claude-3")
  ],
  prompts=[]
)

combined_config = config1 + config2

Error:

def _join_rails_configs(
        base_rails_config: RailsConfig, updated_rails_config: RailsConfig
    ):
        """Helper to join two rails configuration."""
    
        config_old_types = {}
        for model_old in base_rails_config.models:
            config_old_types[model_old.type] = model_old
    
        for model_new in updated_rails_config.models:
            if model_new.type in config_old_types:
                if model_new.engine != config_old_types[model_new.type].engine:
                    raise ValueError(
                        "Both config files should have the same engine for the same model type"
                    )
                if model_new.model != config_old_types[model_new.type].model:
                    raise ValueError(
                        "Both config files should have the same model for the same model type"
                    )
    
        if base_rails_config.actions_server_url != updated_rails_config.actions_server_url:
            raise ValueError("Both config files should have the same actions_server_url")
    
        combined_rails_config_dict = _join_dict(
            base_rails_config.dict(), updated_rails_config.dict()
        )
>       combined_rails_config_dict["config_path"] = ",".join(
            [
                base_rails_config.dict()["config_path"],
                updated_rails_config.dict()["config_path"],
            ]
        )
E       TypeError: sequence item 0: expected str instance, NoneType found

Steps To Reproduce

I ran into this error upstream using the NeMo Guardrails service. Internally, the /v1/chat/completions endpoint invokes RailsConfig.__add__ given multiple config IDs, where I ran into the two errors above.

To reproduce, you can execute the code snippets shared above.

Expected Behavior

Adding two configs does not throw an error in the following cases:

• prompts is None for at least one config
• config_path is None for at least one config

Actual Behavior

Adding two configs does throw an error in the following cases:

• prompts is None for at least one config
• config_path is None for at least one config