## TL;DR
Make the resolver return a real value for that required feature on every input row, adding an explicit fallback or fixing the upstream input feature that was null, because a required feature is declared non-nullable and Chalk fails the whole query when its resolver returns null. Start with the Chalk resolver code and the feature definition that came back null, work on one affected call, record, or run first, and prove the fix there before running the full set. Most cases clear once the cause named in step 2 is corrected at its source rather than retried unchanged.

```text
Chalk resolver failed error "FeatureResolverException: resolver returned null for required feature"
```

## Use this when
- You see this exact message or symptom: Chalk resolver failed error "FeatureResolverException: resolver returned null for required feature"
- One run, record, call, or object is affected and you can name it
- A retry without changing anything reproduces the same result

## Not for this skill when
- The system fails with a different message and none of the signals here appear
- Nothing has failed yet and you are doing first time setup or general planning
- Every service from this vendor is down for all users, which is a vendor outage to wait out first

## Steps
1. Reproduce the failure once using the Chalk resolver code and the feature definition that came back null, and record the time, the workspace or account, and the one item it names. Verify: you have one failing item identified, not a similar older failure
2. Inspect the resolver function for the named feature, the nullability flag on its definition, and the input features it reads for the failing entity. Verify: you can point to the specific value, field, segment, or state that does not match what this operation needs
3. Apply the fix at that source: Make the resolver return a real value for that required feature on every input row, adding an explicit fallback or fixing the upstream input feature that was null, because a required feature is declared non-nullable and Chalk fails the whole query when its resolver returns null. Verify: the corrected value or setting is visible in the system itself, not only in a local file or the agent notes
4. Re-run the original operation on the single affected item first. Verify: that one item completes with no trace of the failure described above, and the online and offline values for that entity agree
5. Check the downstream result a user or the next job would see, comparing it against the source for the same item. Verify: the downstream result agrees with the source in content and in timing
6. Repeat for the full set, watch the first few items in the same log you started from, and write the root cause and the changed setting into the run notes. Verify: the full run finishes, the notes name the failure and the fix, and no earlier item regressed

## Variant phrasings
### Chalk resolver failed error "FeatureResolverException: resolver returned null for required feature"
The subject-first phrasing of the same failure. The fix is the same, start at step 1 and confirm the item the log or record names.
### Tool-first phrasing of this failure
The phrasing searchers use once they know which system raised it. It is the same underlying problem, not a separate bug.
### Why does this keep happening after a retry
The repeat-occurrence phrasing. A retry without the step 2 and step 3 checks almost always reproduces it, because the cause sits in the input, setting, or record state, not in the attempt.

Compatibility: Chalk resolvers in Python, online and offline queries, branch deployments.

## Why it happens
The resolver usually returns null because one of its input features is missing for that entity and the code propagates the null instead of handling it. The exception surfaces at query time, long after the definition compiled cleanly, because nullability is only checked against live inputs.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_DwKAxT-HFkKykLWq5m6QLQ