Fix coder inference for strings.
Fix coder inference for strings.

Empty case statements are no fun.

Change-Id: If00a8569f7de422ab0def4f52a0c791e09d7f1d3
Reviewed-on: https://team-review.git.corp.google.com/135763
Reviewed-by: Henning Rohde <cc74ff07599c64f633a3f6876da4eb88a647f9b9@google.com>
Verified-BuildAndTest: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Verified-Style: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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