Fix NaN check

Author: charleskawczynski

docs/src/dev/compute_convergence.jl

@@ -169,7 +169,9 @@ function compute_convergence!(
     float_str(x) = @sprintf "%.4f" x
     pow_str(x) = "10^{$(@sprintf "%.1f" log10(x))}"
     function si_str(x)
-        x in (0, Inf, -Inf, NaN) && return string(x)
+        if isnan(x) || x in (0, Inf, -Inf)
+            return string(x)
+        end
         exponent = floor(Int, log10(x))
         mantissa = x / 10.0^exponent
         return "$(float_str(mantissa)) \\times 10^{$exponent}"