Invalid extended regular expression error with '.*'

[wholtz]

When I run the following test:

@test "example" {
   load 'test_helper/bats-support/load'
   load 'test_helper/bats-assert/load'
   run echo 'foo'
   assert_output --regexp '.*'
}

The test fails with the message:
Invalid extended regular expression: '.*'

I would expect this test to pass and the regexp looks valid to me.