@Override
        protected boolean shouldConvert(Expression exp) {
            return exp instanceof InputExpression && ((InputExpression)exp).getFieldName() == null;
        }
This processor modifies all indexing scripts so that they input the value of the owning field by default. It also
ensures that all fields used as input exist.

@author Simon Thoresen Hult
config-model/src/main/java/com/yahoo/schema/processing/IndexingInputs.java