googleapis/mcp-toolbox · error

looker API response or its fields object is nil

Error message

looker API response or its fields object is nil

What it means

CheckLookerExploreFields is a nil-guard for the Looker API explore response: it verifies the LookmlModelExplore and its Fields object are non-nil before field extraction, because the Looker SDK can return partial responses where Fields is absent.

Source

Thrown at internal/tools/looker/lookercommon/lookercommon.go:105

			if v.Suggestions != nil && len(*v.Suggestions) > 0 {
				vMap["suggestions"] = *v.Suggestions
			}
			if v.SuggestExplore != nil && v.SuggestDimension != nil {
				vMap["suggest_explore"] = *v.SuggestExplore
				vMap["suggest_dimension"] = *v.SuggestDimension
			}
		}
		logger.DebugContext(ctx, "Converted to %v\n", vMap)
		data = append(data, vMap)
	}

	return data, nil
}

// CheckLookerExploreFields checks if the Fields object in LookmlModelExplore is nil before accessing its sub-fields.
func CheckLookerExploreFields(resp *v4.LookmlModelExplore) error {
	if resp == nil || resp.Fields == nil {
		return fmt.Errorf("looker API response or its fields object is nil")
	}
	return nil
}

func GetFieldParameters() parameters.Parameters {
	modelParameter := parameters.NewStringParameter("model", "The model containing the explore.")
	exploreParameter := parameters.NewStringParameter("explore", "The explore containing the fields.")
	return parameters.Parameters{modelParameter, exploreParameter}
}

func GetQueryParameters() parameters.Parameters {
	modelParameter := parameters.NewStringParameter("model", "The model containing the explore.")
	exploreParameter := parameters.NewStringParameter("explore", "The explore to be queried.")
	fieldsParameter := parameters.NewArrayParameter("fields",
		"The fields to be retrieved.",
		parameters.NewStringParameter("field", "A field to be returned in the query"),
	)
	filtersParameter := parameters.NewMapParameter(

View on GitHub (pinned to 8cc6e09de2)

Solutions

1. Verify the 'model' and 'explore' parameters match real explores in your Looker instance.
2. Check the Looker API credentials and permissions grant access to the explore.
3. Log/inspect the raw response to see why Fields was nil before retrying.

Example fix

// before
explore, _ := sdk.GetLookmlModelExplore(ctx, model, exploreName)
lookercommon.CheckLookerExploreFields(explore)
// after
explore, err := sdk.GetLookmlModelExplore(ctx, model, exploreName)
if err != nil { return err }
if err := lookercommon.CheckLookerExploreFields(explore); err != nil {
    return fmt.Errorf("explore %s/%s unavailable: %w", model, exploreName, err)
}

if explore == nil || explore.Fields == nil {
    return fmt.Errorf("explore response incomplete")
}
// then call CheckLookerExploreFields

func hasExploreFields(resp *v4.LookmlModelExplore) bool {
    return resp != nil && resp.Fields != nil
}

if err := lookercommon.CheckLookerExploreFields(resp); err != nil {
    // surface which model/explore failed and stop field extraction
    return fmt.Errorf("explore %s/%s: %w", model, exploreName, err)
}

When it happens

Trigger: Looker's GetExplore/lookml explore API returns a response whose Fields pointer is nil (explore not found, empty model, or API returning a stub object), then the tool calls this check before accessing resp.Fields.

Common situations: Querying a non-existent explore name/model; Looker instance returning malformed/partial data; SDK version changes altering response population; unauthenticated/limited-access explores.

Related errors

• empty web_server_url in versions payload
• job has no placement info
• unable to get logger from ctx: %s
• unable to parse Timeout string as time.Duration: %s
• client_id and client_secret need to be specified

AI-assisted analysis of googleapis/mcp-toolbox@8cc6e09de2 (2026-09-05). Data as JSON: /api/errors/7e9c56206e37f76a. Report an issue: GitHub.