docs: qualify Function input nullability and local checks

CONTRIBUTING.md

@@ -107,9 +107,9 @@ uv run docs/web-tests/mdx_snippets_gen.py -s docs/web-tests/py -s docs/web-tests
 Review the diff before committing: a few modules currently regenerate with
 unrelated changes, so commit only the snippets for the examples you changed.
 
-Run the examples locally before submitting the change; see `docs/web-tests/README.md`
-for the Python, TypeScript and Rust commands. These examples are not yet wired
-into pull-request CI; that integration remains follow-up work.
+Run the Python, TypeScript and Rust examples in `docs/web-tests/{py,ts,rs}`
+locally before submitting the change. These examples are not yet wired into
+pull-request CI; that integration remains follow-up work.
 
 **Every heading carries an explicit `{#anchor}`.** Those anchors are how the
 Enterprise pages attach their additions to the right section, so they are

docs/web/management/function.mdx

@@ -70,10 +70,15 @@ code:
 {FunctionConnect}
 </CodeBlock>
 
-A column binds to a parameter only when their Arrow types and nullability
-match. `value: float` is non-nullable, so the table declares `value`
-non-nullable; annotate the parameter `Optional[float]` to bind a nullable
-column instead.
+For an ordinary stored input column, the Arrow type must match the parameter.
+A nullable column requires a nullable parameter, such as `Optional[float]`;
+a non-nullable column can bind to either. This example uses `value: float`,
+so the table declares `value` non-nullable.
+
+Computed-column inputs depend on the deployment version. Where supported,
+they bind to non-nullable parameters even though the physical column is
+nullable: refresh skips rows whose computed input is still null. Check your
+deployment's support before using another computed column as an input.
 
 <CodeBlock filename="Python" language="Python" icon="python">
 {FunctionCreateTable}