Rego type error comparing generated object with partial hard coded object

[asleire]

Short description

Play: https://play.openpolicyagent.org/p/1qlgPwcNXA

Snippet:

obj["a"] := input.a

obj["b"] := input.b

test_obj2 if {
	{"a":"1"} == obj with input as {"a": "1"}
}

The code should be valid but gives the following compile error:

1 error occurred: policy.rego:32: rego_type_error: match error
	left  : object<a: string>
	right : object<a: any, b: any>[string: any]

Steps To Reproduce

View play and click "Evaluate"

Expected behavior

I would expect this comparison to be valid since b may be undefined and not part of the object. Evaluating obj with input as {"a": "1"} reveals that it is in fact {"a":"1"}. As such there should be no compile error.