Test mean of empty Union{}-eltyped collections (#40)

Author: tkf

test/runtests.jl

@@ -120,6 +120,10 @@ end
     @test_throws MethodError mean([])
     @test_throws MethodError mean(skipmissing([]))
     @test_throws ArgumentError mean((1 for i in 2:1))
+    if VERSION >= v"1.6.0-DEV.83"
+        @test_throws ArgumentError mean(())
+        @test_throws ArgumentError mean(Union{}[])
+    end
 
     # Check that small types are accumulated using wider type
     for T in (Int8, UInt8)