chore: Update docs-website/reference/haystack-api/classifiers_api.md

[vblagoje]

Our classifiers_api.md contains invalid script sample which fails with:

ValueError                                Traceback (most recent call last)
Cell In[1], line 14
     12 p = Pipeline()
     13 p.add_component(instance=DocumentLanguageClassifier(languages=["en"]), name="language_classifier")
---> 14 p.add_component(instance=MetadataRouter(rules={"en": {"language": {"$eq": "en"}}}), name="router")
     15 p.add_component(instance=DocumentWriter(document_store=document_store), name="writer")
     16 p.connect("language_classifier.documents", "router.documents")

File ~/workspace/haystack/haystack/core/component/component.py:290, in ComponentMeta.__call__(cls, *args, **kwargs)
    288 pre_init_hook = _COMPONENT_PRE_INIT_HOOK.get()
    289 if pre_init_hook is None or pre_init_hook.in_progress:
--> 290     instance = super().__call__(*args, **kwargs)
    291 else:
    292     try:

File ~/workspace/haystack/haystack/components/routers/metadata_router.py:105, in MetadataRouter.__init__(self, rules, output_type)
    103 for rule in self.rules.values():
    104     if "operator" not in rule:
--> 105         raise ValueError(
    106             "Invalid filter syntax. See https://docs.haystack.deepset.ai/docs/metadata-filtering for details."
    107         )
    108 component.set_output_types(self, unmatched=self.output_type, **dict.fromkeys(rules, self.output_type))

ValueError: Invalid filter syntax. See https://docs.haystack.deepset.ai/docs/metadata-filtering for details.

This is a fix for it.

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
haystack-docs	Ignored			Dec 11, 2025 2:27pm

[vblagoje]

@mpangrazzi this is one of those PRs where we are aiming to eventually have fully correct and executable examples in our docs. One markdown document at the time until we have completely verified all docs and keep them in sync. See https://github.com/deepset-ai/haystack-private/issues/182 for more details

[anakin87]

👍