Slice now produces empty pipe for empty slice (fixes #110) (#216)

script.go

@@ -180,8 +180,12 @@ func Post(url string) *Pipe {
 	return NewPipe().Post(url)
 }
 
-// Slice creates a pipe containing each element of s, one per line.
+// Slice creates a pipe containing each element of s, one per line. If s is
+// empty or nil, then the pipe is empty.
 func Slice(s []string) *Pipe {
+	if len(s) == 0 {
+		return NewPipe()
+	}
 	return Echo(strings.Join(s, "\n") + "\n")
 }
 

script_test.go

@@ -1387,6 +1387,18 @@ func TestSliceProducesElementsOfSpecifiedSliceOnePerLine(t *testing.T) {
 	}
 }
 
+func TestSliceGivenEmptySliceProducesEmptyPipe(t *testing.T) {
+	t.Parallel()
+	want := ""
+	got, err := script.Slice([]string{}).String()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want != got {
+		t.Fatalf("want %q, got %q", want, got)
+	}
+}
+
 func TestStdoutReturnsErrorGivenReadErrorOnPipe(t *testing.T) {
 	t.Parallel()
 	brokenReader := iotest.ErrReader(errors.New("oh no"))