all: sync with master

internal/aghalg/aghalg.go

@@ -10,6 +10,20 @@ import (
 	"golang.org/x/exp/slices"
 )
 
+// Coalesce returns the first non-zero value.  It is named after the function
+// COALESCE in SQL.  If values or all its elements are empty, it returns a zero
+// value.
+func Coalesce[T comparable](values ...T) (res T) {
+	var zero T
+	for _, v := range values {
+		if v != zero {
+			return v
+		}
+	}
+
+	return zero
+}
+
 // UniqChecker allows validating uniqueness of comparable items.
 //
 // TODO(a.garipov): The Ordered constraint is only really necessary in Validate.