Fix potential bug caught by gobugs

[imjasonh]

The two-arg form of make results in a slice with n empty elements, which we then append to, resulting in a slice with empty elements.

Instead of trying to remember to use the correct form for make (i.e., make([]string, 0, len(x))), just avoid the premature optimization and declare an empty slice without capacity.

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[dlorenc]

/lgtm

[dlorenc]

/approve

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