panic when mutiple assign to multi documents

[care0717]

Describe the bug
I've got panic when I use multiple assign to multi documents.

Version of yq: 4.25.2
Operating system: mac
Installed via: homebrew

Input Yaml
sample.yml:

a: 1
---
b: 2

Command

yq '. *= {"c":3}' sample.yaml

Actual behavior
output

a: 1
c: 3
panic: interface conversion: interface {} is nil, not yqlib.multiplyPreferences

goroutine 1 [running]:
github.com/mikefarah/yq/v4/pkg/yqlib.multiplyOperator(0xc000013890?, {0xc0004612f0, 0xc000461380, 0x1, {0x0, 0x0}}, 0xc0003b8c30)
	github.com/mikefarah/yq/v4/pkg/yqlib/operator_multiply.go:37 +0x205
github.com/mikefarah/yq/v4/pkg/yqlib.(*dataTreeNavigator).GetMatchingNodes(0xc000461380?, {0xc0004612f0, 0xc000461380, 0x1, {0x0, 0x0}}, 0xc0003b8c30)
	github.com/mikefarah/yq/v4/pkg/yqlib/data_tree_navigator.go:37 +0x25c
github.com/mikefarah/yq/v4/pkg/yqlib.resultsForRHS(0x19?, {0xc0004612f0, 0xc000461380, 0x1, {0x0, 0x0}}, 0x28?, {0x0, 0x0, 0xc00045e920}, ...)
	github.com/mikefarah/yq/v4/pkg/yqlib/operators.go:69 +0x1fc
github.com/mikefarah/yq/v4/pkg/yqlib.doCrossFunc(0x1d?, {0xc0004612f0, 0xc000461380, 0x1, {0x0, 0x0}}, 0xc0003b8c48, {0x0, 0x0, 0xc00045e920})
	github.com/mikefarah/yq/v4/pkg/yqlib/operators.go:125 +0x413
github.com/mikefarah/yq/v4/pkg/yqlib.crossFunctionWithPrefs(0x1?, {0xc000461260, 0x0, 0x1, {0x0, 0x0}}, 0x1e00108?, {0x0, 0x0, 0xc00045e920})
	github.com/mikefarah/yq/v4/pkg/yqlib/operators.go:158 +0x3db
github.com/mikefarah/yq/v4/pkg/yqlib.crossFunction(0x110230f?, {0xc000461260, 0x0, 0x1, {0x0, 0x0}}, 0xc0003b8c18?, 0x0?, 0xf0?)
	github.com/mikefarah/yq/v4/pkg/yqlib/operators.go:136 +0x9f
github.com/mikefarah/yq/v4/pkg/yqlib.assignUpdateOperator(0xc000013890?, {0xc000460ed0, 0x0, 0x0, {0x0, 0x0}}, 0xc0003b8c48)
	github.com/mikefarah/yq/v4/pkg/yqlib/operator_assign.go:31 +0x305
github.com/mikefarah/yq/v4/pkg/yqlib.(*dataTreeNavigator).GetMatchingNodes(0xc0003b8c00?, {0xc000460ed0, 0x0, 0x0, {0x0, 0x0}}, 0xc0003b8c48)
	github.com/mikefarah/yq/v4/pkg/yqlib/data_tree_navigator.go:37 +0x25c
github.com/mikefarah/yq/v4/pkg/yqlib.compoundAssignFunction(0x13a0020?, {0xc000460ed0, 0x0, 0x0, {0x0, 0x0}}, 0xc0003b8840, 0xc0004276f0)
	github.com/mikefarah/yq/v4/pkg/yqlib/operators.go:35 +0x3ba
github.com/mikefarah/yq/v4/pkg/yqlib.multiplyAssignOperator(0xc000013890?, {0xc000460ed0, 0x0, 0x0, {0x0, 0x0}}, 0x0?)
	github.com/mikefarah/yq/v4/pkg/yqlib/operator_multiply.go:32 +0xe8
github.com/mikefarah/yq/v4/pkg/yqlib.(*dataTreeNavigator).GetMatchingNodes(0x0?, {0xc000460ed0, 0x0, 0x0, {0x0, 0x0}}, 0xc0003b8840)
	github.com/mikefarah/yq/v4/pkg/yqlib/data_tree_navigator.go:37 +0x25c
github.com/mikefarah/yq/v4/pkg/yqlib.(*streamEvaluator).Evaluate(0xc000427cf0, {0x7ffeefbff948, 0xb}, {0x143cc20?, 0xc0003ddf80?}, 0x1fe52c0?, {0x143e8d0, 0xc0003dde60}, {0x0, 0x0}, ...)
	github.com/mikefarah/yq/v4/pkg/yqlib/stream_evaluator.go:124 +0x35c
github.com/mikefarah/yq/v4/pkg/yqlib.(*streamEvaluator).EvaluateFiles(0xc000010018?, {0x7ffeefbff93b, 0xc}, {0xc00006e610, 0x1, 0x6?}, {0x143e8d0, 0xc0003dde60}, 0x2?, {0x143dde0, ...})
	github.com/mikefarah/yq/v4/pkg/yqlib/stream_evaluator.go:73 +0x30e
github.com/mikefarah/yq/v4/cmd.evaluateSequence(0xc000015900?, {0xc00006e600, 0x2, 0x2})
	github.com/mikefarah/yq/v4/cmd/evalute_sequence_command.go:132 +0x8a5
github.com/spf13/cobra.(*Command).execute(0xc000015900, {0xc00006e5a0, 0x2, 0x2})
	github.com/spf13/cobra@v1.4.0/command.go:856 +0x67c
github.com/spf13/cobra.(*Command).ExecuteC(0xc000015680)
	github.com/spf13/cobra@v1.4.0/command.go:974 +0x3b4
github.com/spf13/cobra.(*Command).Execute(...)
	github.com/spf13/cobra@v1.4.0/command.go:902
main.main()
	github.com/mikefarah/yq/v4/yq.go:22 +0x1f1

Expected behavior

a: 1
c: 3
---
b: 2
c: 3