Subject failed to notify listener Error: Unexpected key type (type: undefined, value: undefined)

[philipp-classen]

subject.js:34 WTM [reporting] error: Subject failed to notify listener Error: Unexpected key type (type: undefined, value: undefined)
    at ChromeStorageMap.normalizeKey (chrome-storage-map.js:190:11)
    at ChromeStorageMap.get (chrome-storage-map.js:93:22)
    at TokenPipeline.getFromCache (cached-entry-pipeline.js:57:28)
    at TokenPipeline.get (cached-entry-pipeline.js:36:24)
    at index.js:119:38
    at subject.js:32:9
    at Set.forEach (<anonymous>)
    at Subject.pub (subject.js:30:20)
    at index.js:100:22

token can be undefined (code:

webextension-packages/packages/reporting/src/request/steps/token-telemetry/index.js

Line 118 in e00ff43

const tokenStats = this.tokens.get(token);

)

// process a batch of entries for a specific token
const token = batch[0].token;

const tokenStats = this.tokens.get(token);

batch is an array of strings. Entries look like that 513d8f49d55a9708:3a2d7564baee79182ebc7b75084aabd3 (all the 120 entries in my example look like that).

The string have no .token field, which explains the that the lookup in the ChromeStorageMap fails. The question is how to derive the key correctly?

Browser: Opera 108 on Linux.