[BUG] Crash on conflict

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

npm ERR! Cannot read properties of null (reading 'edgesOut')

npm ERR! A complete log of this run can be found in:
npm ERR!     .npm/_logs/2022-07-12T14_15_56_150Z-debug-0.log

87 verbose stack TypeError: Cannot read properties of null (reading 'edgesOut')
87 verbose stack     at [loadPeerSet] (/usr/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:1359:38)
87 verbose stack     at async [buildDepStep] (/usr/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:976:11)
87 verbose stack     at async Arborist.buildIdealTree (/usr/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:218:7)
87 verbose stack     at async Promise.all (index 1)
87 verbose stack     at async Arborist.reify (/usr/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/reify.js:153:5)
87 verbose stack     at async Install.exec (/usr/lib/node_modules/npm/lib/commands/install.js:145:5)
87 verbose stack     at async module.exports (/usr/lib/node_modules/npm/lib/cli.js:78:5)
88 verbose cwd /tmp/crash
89 verbose Linux 5.15.0-40-generic
90 verbose node v18.4.0
91 verbose npm  v8.13.2
92 error Cannot read properties of null (reading 'edgesOut')

Expected Behavior

Expected to see errors about conflicting versions.

Steps To Reproduce

Steps to reproduce:

mkdir crash
cd crash
npm install @nestjs/platform-express@8
npm install @nestjs/core

Environment

• npm: 8.13.2
• Node.js: v18.4.0
• OS Name: Ubuntu 22.04 LTS

Start by running the listed npm install reproduction with npm 8.13.2, then inspect [loadPeerSet] and [buildDepStep] in node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js. Trace how the conflict reaches Arborist.reify in reify.js. Done means the reproduction reports conflicting versions instead of crashing on a null edgesOut value.