avoid `empty body` warnings emposed by default activation of `expandEmptyElements`

[Pankraz76]

It would be nice to avoid empty body warnings emposed by default activation of expandEmptyElements, by disabling default value for this property.

make false:

spotless/lib/src/main/java/com/diffplug/spotless/pom/SortPomCfg.java

Line 30 in 2cc8c04

public boolean expandEmptyElements = true;

need:

<sortPom/>

have:

<sortPom>
  <expandEmptyElements>false</expandEmptyElements>
</sortPom>

reproducer:

• Fix #5770: [java] Spotless:SortPom pmd/pmd#5846