[Fix] Stop pagination on empty next page token (#343)

## Changes
Stop pagination on empty next page token

## Tests
<!-- How is this tested? -->

.codegen/api.java.tmpl

@@ -172,7 +172,7 @@ public class {{.PascalName}}API {
  {{- else if .Pagination.Token -}}
  {
  String token = response.get{{.Pagination.Token.Bind.PascalName}}();
- if (token == null) {
+ if (token == null || token.isEmpty()) {
  return null;
  }
  return request.set{{.Pagination.Token.PollField.PascalName}}(token);