Trailing comma in unpackTypes causes empty string element and confusing error

## Description

In `EarMojo.java:460`, a trailing comma in the `unpackTypes` parameter produces an empty string element:

```java
unpackTypesList = Arrays.asList(unpackTypes.split(","));
```

If the user configures `unpackTypes = "jar,war,"`, `split(",")` produces the array `["jar", "war", ""]`. The empty string `""` will fail `isStandardArtifactType()` and produce a confusing error message.

## Expected behavior

Filter out empty strings: