Cannot read property 'maneuverability' of null

Uncaught (in promise) TypeError: Cannot read property 'maneuverability' of null
    at ActorPF._addDefaultChanges (entity.js:551)
    at ActorPF._updateChanges (entity.js:846)
    at pf1.js:103
    at Array.forEach (<anonymous>)
    at pf1.js:103
    at Function._call (foundry.js:2045)
    at Function.callAll [as __furnace_original_callAll] (foundry.js:2005)
    at Function.callOriginalFunction (Patches.js:56)
    at Function.<anonymous> (Debug.js:33)
    at Game.setupGame (foundry.js:5184)

offending area:

line 551
// Add fly bonuses or penalties based on maneuverability
    const flyKey = data.data.attributes.speed.fly.maneuverability;
    const flyValue = CONFIG.PF1.flyManeuverabilityValues[flyKey];
    if (flyValue !== 0) {
      changes.push({
        raw: [flyValue.toString(), "skill", "skill.fly", "untyped", 0],
        source: {
          name: "Maneuverability"
        }
      });
    }