News and compat annotation for #29033 (mean and var for empty iterators).

Author: fredrikekre

NEWS.md

@@ -75,6 +75,7 @@ Standard library changes
   * `merge(::NamedTuple, ::NamedTuple...)` can now be used with more than 2 `NamedTuple`s ([#29259]).
   * `Future.copy!` has been moved to `Base` ([#29178]).
   * New `ncodeunits(c::Char)` method as a fast equivalent to `ncodeunits(string(c))` ([#29153]).
+  * `mean` and `var` now handles the empty case ([#29033]).
 
 Compiler/Runtime improvements
 -----------------------------

stdlib/Statistics/src/Statistics.jl

@@ -109,6 +109,9 @@ end
 
 Compute the mean of an array over the given dimensions.
 
+!!! compat "Julia 1.1"
+    `mean` for empty arrays requires at least Julia 1.1.
+
 # Examples
 ```jldoctest
 julia> A = [1 2; 3 4]