fix: Prevent null snapshots from being stored and causing errors (#16015

)

packages/driver/cypress/integration/cypress/log_spec.js

@@ -24,6 +24,16 @@ describe('src/cypress/log', function () {
       expect(result).to.equal(log)
     })
 
+    // https://github.com/cypress-io/cypress/issues/15816
+    it('does not add snapshot if createSnapshot returns null', function () {
+      this.cy.createSnapshot.returns(null)
+
+      const log = this.log()
+      const result = log.snapshot()
+
+      expect(result.get('snapshots')).to.have.length(0)
+    })
+
     it('is no-op if not interactive', function () {
       this.config.withArgs('isInteractive').returns(false)
 

packages/driver/src/cy/snapshots.js

@@ -158,6 +158,9 @@ const create = ($$, state) => {
       // are no side effects from cloning it. see below for how we re-attach
       // it to the AUT document
       // https://github.com/cypress-io/cypress/issues/8679
+      // this can fail if snapshotting before the page has fully loaded,
+      // so we catch this below and return null for the snapshot
+      // https://github.com/cypress-io/cypress/issues/15816
       const $body = $$(snapshotDocument.importNode($$('body')[0], true))
 
       // for the head and body, get an array of all CSS,

packages/driver/src/cypress/log.js

@@ -329,8 +329,13 @@ const Log = function (cy, state, config, obj) {
 
       const snapshots = this.get('snapshots') || []
 
-      // insert at index 'at' or whatever is the next position
-      snapshots[options.at || snapshots.length] = snapshot
+      // don't add snapshot if we couldn't create one, which can happen
+      // if the snapshotting process errors
+      // https://github.com/cypress-io/cypress/issues/15816
+      if (snapshot) {
+        // insert at index 'at' or whatever is the next position
+        snapshots[options.at || snapshots.length] = snapshot
+      }
 
       this.set('snapshots', snapshots)