Fix uses of code that are not supported by Xpress v8

[odow]

x-ref #220

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 68.13%. Comparing base (1b075d1) to head (d274a71).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #258 +/- ## ========================================== + Coverage 68.08% 68.13% +0.04% ========================================== Files 6 6 Lines 3290 3295 +5 ========================================== + Hits 2240 2245 +5 Misses 1050 1050 ```

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