Generate UUIDArray from template

- Fix error in Set
- Specifically handle untyped nil

pgtype/typed_array.go.erb

@@ -15,6 +15,12 @@ type <%= pgtype_array_type %> struct {
 }
 
 func (dst *<%= pgtype_array_type %>) Set(src interface{}) error {
+	// untyped nil and typed nil interfaces are different
+	if src == nil {
+		*dst = <%= pgtype_array_type %>{Status: Null}
+		return nil
+	}
+
 	switch value := src.(type) {
 	<% go_array_types.split(",").each do |t| %>
 	case <%= t %>:
@@ -40,7 +46,7 @@ func (dst *<%= pgtype_array_type %>) Set(src interface{}) error {
 		if originalSrc, ok := underlyingSliceType(src); ok {
 			return dst.Set(originalSrc)
 		}
-		return errors.Errorf("cannot convert %v to <%= pgtype_element_type %>", value)
+		return errors.Errorf("cannot convert %v to <%= pgtype_array_type %>", value)
 	}
 
 	return nil