Fixed small bug

[codecov[bot]]

Codecov Report

Base: 88.15% // Head: 87.87% // Decreases project coverage by -0.28% :warning:

Coverage data is based on head (8e4b61b) compared to base (4ebd61b). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #197 +/- ## ========================================== - Coverage 88.15% 87.87% -0.29% ========================================== Files 28 23 -5 Lines 3377 2457 -920 ========================================== - Hits 2977 2159 -818 + Misses 400 298 -102 ``` | [Impacted Files](https://codecov.io/gh/opencadc/cadctools/pull/197?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc) | Coverage Δ | | |---|---|---| | [cadctap/cadctap/core.py](https://codecov.io/gh/opencadc/cadctools/pull/197/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc#diff-Y2FkY3RhcC9jYWRjdGFwL2NvcmUucHk=) | | | | [cadcdata/cadcdata/core.py](https://codecov.io/gh/opencadc/cadctools/pull/197/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc#diff-Y2FkY2RhdGEvY2FkY2RhdGEvY29yZS5weQ==) | | | | [cadcutils/cadcutils/\_\_init\_\_.py](https://codecov.io/gh/opencadc/cadctools/pull/197/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc#diff-Y2FkY3V0aWxzL2NhZGN1dGlscy9fX2luaXRfXy5weQ==) | | | | [cadcdata/cadcdata/\_\_init\_\_.py](https://codecov.io/gh/opencadc/cadctools/pull/197/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc#diff-Y2FkY2RhdGEvY2FkY2RhdGEvX19pbml0X18ucHk=) | | | | [cadctap/cadctap/\_\_init\_\_.py](https://codecov.io/gh/opencadc/cadctools/pull/197/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc#diff-Y2FkY3RhcC9jYWRjdGFwL19faW5pdF9fLnB5) | | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opencadc)

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