Inscrutable durableMapStore.get(deviceNode) exception for a missing key

[michaelfig]

Describe the bug

@FUDCo writes:

Trying to get something that’s not there from a MapStore is an error while doing the same from a Map returns undefined, and though you do get an error (per spec), the specific error you happen to get is sort of incidental and not very useful for purposes of diagnosing what’s the matter.

To Reproduce

Steps to reproduce the behavior:
0. do this in a new SwingSet vat

1. Create a fresh durableMapStore (called dms in this recipe)
2. execute dms.get(device) where device is a device not otherwise used by the vat
3. See error ending with:

2023-03-01T22:36:16.655Z SwingSet: ls: v9: Logging sent error stack (Error#1)
2023-03-01T22:36:16.655Z SwingSet: ls: v9: Error#1: no ordinal for Object [Alleged: device] {}
2023-03-01T22:36:16.655Z SwingSet: ls: v9: Error: no ordinal for (an object)
 at construct ()
 at Error (/bundled-source/.../node_modules/ses/src/error/tame-error-constructor.js:56)
 at makeError (/bundled-source/.../node_modules/ses/src/error/assert.js:242)
 at fail (/bundled-source/.../node_modules/ses/src/error/assert.js:370)
 at encodeRemotable (/bundled-source/.../packages/swingset-liveslots/src/collectionManager.js:233)
 at encodePassable (/bundled-source/.../node_modules/@endo/marshal/src/encodePassable.js:348)
 at keyToDBKey (/bundled-source/.../packages/swingset-liveslots/src/collectionManager.js:278)

Expected behavior

dms.get(device) should throw with something like:

Error#1: key not found: [Alleged: device] {}

Platform Environment

• what OS are you using? what version of Node.js? MacOS w/ Node.js 16.18.1
• is there anything special/unusual about your platform? not pertinent to this problem
• what version of the Agoric-SDK are you using? agoric-upgrade-8-1037-g80de089d3

Additional context

I suspect the existing tests use the MapStore "properly" so they didn't see this exception.

If I do the proper MapStore membership check first, then the error is avoided:

const value = dms.has(device) ? dms.get(device) : undefined;