If textAsset is always null, it can mean two things (due to your code):
- The file
hfba_25 doesn't exist in the Resources subdir;
- The file does exist, but can't be cast as a
TextAsset.
To check which of the two is true, you need to change the code to this:
TextAsset textAsset = (TextAsset)Resources.Load(filePath);
Debug.Log(textAsset);
then run inside Unity and check the console.
If you just get Null, then it means that it's 1 (file doesn't exist).
If instead you get InvalidCastException: Specified cast is not valid., then it means it's 2, the file exists but it can't be cast as a TextAsset type.
This happens because in C#, if you cast using the keyword as, when the cast is invalid you don't get an exception, but instead the reference is just set to null.