Warn and normalize when source_rendering_behavior=None is passed

[pankajastro]

Python does not enforce type annotations at runtime, so passing None for source_rendering_behavior bypasses the SourceRenderingBehavior.NONE default, causing sources to be rendered incorrectly and an AttributeError in converter.py when .value is called on None.

Add a guard in RenderConfig.post_init that issues a UserWarning and normalizes None to SourceRenderingBehavior.NONE, consistent with the existing deprecation warning pattern in post_init.

DAG

example_watcher = DbtDag(
    # dbt/cosmos-specific parameters
    execution_config=ExecutionConfig(
        execution_mode=ExecutionMode.WATCHER,
    ),
    project_config=ProjectConfig(jaffle_shop_path),
    render_config=RenderConfig(source_rendering_behavior=None), 
    profile_config=default_profile,
    # normal dag parameters
    schedule="@daily",
    start_date=datetime(2023, 1, 1),
    catchup=False,
    dag_id="example_watcher",
    default_args={"retries": 0},
    operator_args={
        "dbt_cmd_flags": ["--log-level", "debug"],
    },
)

Before change DAG topology

After Change DAG topology

closes: #2568

[Copilot]

Pull request overview

This PR fixes a runtime misconfiguration edge case in Cosmos RenderConfig where passing source_rendering_behavior=None bypasses the intended default (SourceRenderingBehavior.NONE), leading to incorrect source rendering and downstream AttributeErrors when .value is accessed.

Changes:

• Add a RenderConfig.__post_init__ guard that warns when source_rendering_behavior=None is provided and normalizes it to SourceRenderingBehavior.NONE.
• Add a unit test asserting the warning is emitted and the value is normalized.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cosmos/config.py	Normalizes source_rendering_behavior=None to SourceRenderingBehavior.NONE and emits a UserWarning to prevent incorrect rendering/telemetry errors.
tests/test_config.py	Adds coverage to ensure the new warning + normalization behavior is enforced.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.05%. Comparing base (aa4c770) to head (6168966).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2570   +/-   ##
=======================================
  Coverage   98.04%   98.05%           
=======================================
  Files         103      103           
  Lines        7589     7592    +3     
=======================================
+ Hits         7441     7444    +3     
  Misses        148      148           

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