Util: Modify SplitHostPortDefault not to return an error for empty input (#20351)

* Util: Optionally allow empty input in SplitHostPortDefault

Due to a recent change the SQL Server tests failed because passing an
empty datasource url in `util.SplitHostPortDefault` was no more allowed.
This fix contains the following modifications:
- Modifies the util.SplitHostPortDefault not to return an error for empty input.
- Modifies the util.SplitHostPort to return an error for empty input.
- Introduces an additional test for empty input.

pkg/util/ip_address.go

@@ -44,7 +44,7 @@ func SplitHostPortDefault(input, defaultHost, defaultPort string) (NetworkAddres
 		Port: defaultPort,
 	}
 	if len(input) == 0 {
-		return addr, fmt.Errorf("Input is empty")
+		return addr, nil
 	}
 
 	start := 0
@@ -82,5 +82,8 @@ func SplitHostPortDefault(input, defaultHost, defaultPort string) (NetworkAddres
 
 // SplitHostPort splits ip address/hostname string by host and port
 func SplitHostPort(input string) (NetworkAddress, error) {
+	if len(input) == 0 {
+		return NetworkAddress{}, fmt.Errorf("Input is empty")
+	}
 	return SplitHostPortDefault(input, "", "")
 }

pkg/util/ip_address_test.go

@@ -87,6 +87,11 @@ func TestSplitHostPortDefault(t *testing.T) {
 		So(err, ShouldBeNil)
 		So(addr.Host, ShouldEqual, "xyz.rds.amazonaws.com")
 		So(addr.Port, ShouldEqual, "123")
+
+		addr, err = SplitHostPortDefault("", "localhost", "1433")
+		So(err, ShouldBeNil)
+		So(addr.Host, ShouldEqual, "localhost")
+		So(addr.Port, ShouldEqual, "1433")
 	})
 }