Add if else check on state_vector in _new_target function

[codecov[bot]]

Codecov Report

Base: 94.94% // Head: 94.70% // Decreases project coverage by -0.24% :warning:

Coverage data is based on head (b8afc4b) compared to base (15ede0f). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #755 +/- ## ========================================== - Coverage 94.94% 94.70% -0.25% ========================================== Files 171 174 +3 Lines 8464 9193 +729 Branches 1233 1411 +178 ========================================== + Hits 8036 8706 +670 - Misses 317 349 +32 - Partials 111 138 +27 ``` | Flag | Coverage Δ | | |---|---|---| | integration | `70.53% <100.00%> (+0.74%)` | :arrow_up: | | unittests | `89.43% <33.33%> (-2.63%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/dstl/Stone-Soup/pull/755?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl) | Coverage Δ | | |---|---|---| | [stonesoup/simulator/simple.py](https://codecov.io/gh/dstl/Stone-Soup/pull/755/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#diff-c3RvbmVzb3VwL3NpbXVsYXRvci9zaW1wbGUucHk=) | `98.02% <100.00%> (+0.02%)` | :arrow_up: | | [stonesoup/base.py](https://codecov.io/gh/dstl/Stone-Soup/pull/755/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#diff-c3RvbmVzb3VwL2Jhc2UucHk=) | `96.20% <0.00%> (ø)` | | | [stonesoup/plotter.py](https://codecov.io/gh/dstl/Stone-Soup/pull/755/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#diff-c3RvbmVzb3VwL3Bsb3R0ZXIucHk=) | `90.19% <0.00%> (ø)` | | | [stonesoup/\_\_init\_\_.py](https://codecov.io/gh/dstl/Stone-Soup/pull/755/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dstl#diff-c3RvbmVzb3VwL19faW5pdF9fLnB5) | `83.33% <0.00%> (ø)` | | 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=dstl). 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=dstl)

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