or

The falsy values are false, 0, any nil pointer or interface value, any array, slice, map, or string of length zero, and zero time.Time values.

Everything else is truthy.

The or function evaluates the arguments from left to right, and returns when the result is determined.

{{ or 0 1 2 }} → 1 (int)
{{ or false "a" 1 }} → a (string)
{{ or 0 true "a" }} → true (bool)

{{ or false "" 0 }} → 0 (int)
{{ or 0 "" false }} → false (bool)

{{ or true (math.Div 1 0) }} → true (bool)

See Go’s text/template documentation for more information.