Data value cannot be added without a site

jirikadlec2[CodePlex]
I set-up a new hydroserver.
I create a new source.
I don't have any sites on the hydroserver.
I go to the Add Single Value, Add Multiple Values, or Import Data File page.
The add_data_value.php, add_multiple_values.php and import_data_file.php pages don't work.

There should be an info/warning/error message on the pages add_data_value.php, add_multiple_values.php and import_data_file.php saying that data values cannot be added without a site

Start with add_data_value.php, add_multiple_values.php, and import_data_file.php and reproduce each page on a HydroServer with a source but no sites. Confirm the current failure path, then ensure each page displays an info, warning, or error message explaining that data values require a site; done means all three pages provide that guidance instead of failing silently.

Written by the indexing model from the issue text.