This isn't exactly a "link" but a simple mailmerge. What you want is an IF field.

This example shows a mergefield named Field1. It prints:
Field 1: contents of field 1
on a separate line if, and only if, there are contents in field1.

If field1 can be a negative number you would want the condition to be <> 0.

Turn on display of field codes when writing fields. Alt-F9

This is what the fields will look like. Note the line break in the middle of the IF field which is actually a paragraph mark in Word.

{ IF { MERGEFIELD Field1 } > 0 "Field1: { MERGEFIELD Field1}
" "" }

Note the braces {} cannot be typed in from the keyboard. They have to be inserted by Word. They come in pairs. They are inserted when you add a merge field or a regular field. You can make your own fields with Ctrl-F9 which inserts a pair.