Add handling for attachement None

[kkappler]

Two errors encountered in issue #156

• [x] Add handling for attachment None Fixed attachment None error in the sense that the TF loads. It is not clear if the attachment is supposed to be allowed to have the value None. @kujaku11 Can you check if this. The TF is attached to issue #156 .

• [x] Error parsing orientation

[codecov-commenter]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.01% :warning:

Comparison is base (ae462a0) 81.74% compared to head (a7d8af4) 81.74%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## fcs #157 +/- ## ========================================== - Coverage 81.74% 81.74% -0.01% ========================================== Files 264 264 Lines 18331 18333 +2 ========================================== + Hits 14985 14986 +1 - Misses 3346 3347 +1 ``` | [Files Changed](https://app.codecov.io/gh/kujaku11/mt_metadata/pull/157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JP) | Coverage Δ | | |---|---|---| | [...ansfer\_functions/io/emtfxml/metadata/attachment.py](https://app.codecov.io/gh/kujaku11/mt_metadata/pull/157?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=JP#diff-bXRfbWV0YWRhdGEvdHJhbnNmZXJfZnVuY3Rpb25zL2lvL2VtdGZ4bWwvbWV0YWRhdGEvYXR0YWNobWVudC5weQ==) | `93.75% <50.00%> (-6.25%)` | :arrow_down: |

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[kujaku11]

This issue has been fixed with commit https://github.com/kujaku11/mt_metadata/commit/cd25167b09529d741a60bf545c8ba192a16a77f0. Therefore the pull request has been closed.