Summary
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Modify implementation such that `java.nio.file.Path.of(String first, String... more)` and `java.nio.file.Paths.get(String first, String... more)` throw a `NullPointerException` when `first` is `null`.

Problem
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The package specification of `java.nio.file` states that

```Unless otherwise noted, passing a null argument to a constructor or method of any class or interface in this package will cause a NullPointerException to be thrown.```

but the aforementioned methods do not throw a `NullPointerException`. This is incorrect behavior not only due to failing to throw the exception, but more in terms of allowing a corrupted path name containing the string `"null"` to be created. This could lead to unexpected and possibly confusing behavior.

Solution
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Modify the implementations of `getPath(String first, String... more)` in the `UnixFileSystem` and `WindowsFileSystem` classes in the internal `sun.nio.fs` package such that they throw `NullPointerException` if the first parameter `first` is `null`. `Paths.get` calls `Path.of()` which calls `XFileSystem.getPath()`.

Specification
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There is no change to the existing specification per se.