Finding a null followed by a see cref ports them without space

Example: https://github.com/dotnet/dotnet-api-docs/pull/8478/files#r991548195

Actual:
```xml
<see langword="null" /><see cref="F:Microsoft.Extensions.Options.Options.DefaultName" />
```

Expected:
```
<see langword="null" /> <see cref="F:Microsoft.Extensions.Options.Options.DefaultName" />
```