Unused empty capture group in regex pattern #67

Description

In MappingUtils.java:90, the RegexBasedInterpolator is constructed with:

new RegexBasedInterpolator("\\@\\{(", ")?([^}]+)\\}@");

The prefix contains an opening ( and the suffix starts with )?, forming an empty optional capture group ()? that spans across the interpolator's internal key capture pattern. This group is never used for anything and is functionally dead regex.

The same result could be achieved with the simpler:

new RegexBasedInterpolator("\\@\\{", "\\}@");

Impact

No functional impact, but the unnecessary complexity obscures the intent and may confuse future contributors.

Relevant code

src/main/java/org/apache/maven/shared/mapping/MappingUtils.java:90