Fix Array#sample for [] when called without n and a Random is given

Author: bjfish

CHANGELOG.md

@@ -15,6 +15,7 @@ Bug fixes:
 * Fix a resource leak from allocators defined in C extensions (@aardvark179).
 * `SIGINT`/`Interrupt`/`Ctrl+C` now shows the backtrace and exits as signaled, like CRuby (@eregon).
 * Update patch feature finding to prefer the longest matching load path (#2605, @bjfish).
+* Fix `Array#sample` for `[]` when called without `n` and a `Random` is given (#2612, @bjfish).
 
 Compatibility:
 

spec/ruby/core/array/sample_spec.rb

@@ -19,10 +19,18 @@
     [].sample.should be_nil
   end
 
+  it "returns nil for an empty array when called without n and a Random is given" do
+    [].sample(random: Random.new(42)).should be_nil
+  end
+
   it "returns a single value when not passed a count" do
     [4].sample.should equal(4)
   end
 
+  it "returns a single value when not passed a count and a Random is given" do
+    [4].sample(random: Random.new(42)).should equal(4)
+  end
+
   it "returns an empty Array when passed zero" do
     [4].sample(0).should == []
   end

src/main/ruby/truffleruby/core/array.rb

@@ -1050,7 +1050,10 @@ def sample(count=undefined, options=undefined)
       rng = Kernel
     end
 
-    return at rng.rand(size) unless count
+    size = self.size
+    unless count
+      return at(size < 2 ? 0 : rng.rand(size))
+    end
 
     count = size if count > size