@Override
    protected E applyStringOperation(String item) {
        return (E) getTrimmedString(item, true, true);
    }
Reference implementation for trim() step, a mid-traversal step which returns a string with leading and trailing
whitespace removed. Null values are not processed and remain as null when returned.
If the incoming traverser is a non-String value then an {@code IllegalArgumentException} will be thrown.

@author David Bechberger (http://bechberger.com)
@author Yang Xia (http://github.com/xiazcy)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/TrimLocalStep.java