[GH-11032] Bug - Allow query parameters than contain spaces for Java client. (#11160)

The java client doesn't allow query parameters that have a value of just "%20"
or "%0A". Those can now be values with this commit.

modules/openapi-generator/src/main/resources/Java/Pair.mustache

@@ -41,10 +41,6 @@ public class Pair {
             return false;
         }
 
-        if (arg.trim().isEmpty()) {
-            return false;
-        }
-
         return true;
     }
 }