Add fix to the full cache issue

[codecov[bot]]

Codecov Report

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

Comparison is base (74c346f) 99.39% compared to head (ba8af9f) 99.39%.

:exclamation: Current head ba8af9f differs from pull request most recent head b6a314d. Consider uploading reports for the commit b6a314d to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #99 +/- ## ======================================== Coverage 99.39% 99.39% ======================================== Files 9 9 Lines 494 496 +2 ======================================== + Hits 491 493 +2 Misses 3 3 ``` | [Files](https://app.codecov.io/gh/OHDSI/DeepPatientLevelPrediction/pull/99?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OHDSI) | Coverage Δ | | |---|---|---| | [R/Estimator.R](https://app.codecov.io/gh/OHDSI/DeepPatientLevelPrediction/pull/99?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OHDSI#diff-Ui9Fc3RpbWF0b3IuUg==) | `100.00% <100.00%> (ø)` | | | [R/TrainingCache-class.R](https://app.codecov.io/gh/OHDSI/DeepPatientLevelPrediction/pull/99?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=OHDSI#diff-Ui9UcmFpbmluZ0NhY2hlLWNsYXNzLlI=) | `95.00% <100.00%> (+0.26%)` | :arrow_up: |

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