BaseFilter.loadProperties() silently skips null/empty filter file entries

In `src/main/java/org/apache/maven/shared/filtering/BaseFilter.java`, line 192:

```
if (filterFile == null || filterFile.trim().isEmpty()) {
// skip empty file name
continue;
}
```

Null or empty entries in the filters list are silently skipped. If a caller accidentally includes an empty string in their filter list (e.g., from a malformed POM), no warning or error is logged. The problem is silently masked.

Start in src/main/java/org/apache/maven/shared/filtering/BaseFilter.java around line 192 and trace how null or empty filter entries are handled. Check the existing tests for BaseFilter.loadProperties() before choosing the project's expected reporting behavior. Done means malformed entries are no longer silently masked and the behavior is covered by tests.

Written by the indexing model from the issue text.