docs: private FieldIndex registerFieldIndex(final int index,
                                            final InternalReadAccessor fieldExtractor) {
          FieldIndex fieldIndex = null;
  
          // is linkedlist null, if so create and add
          if ( this.hashedFieldIndexes == null ) {
              this.hashedFieldIndexes = new LinkedList<FieldIndex>();
              fieldIndex = new FieldIndex( index,
                                           fieldExtractor );
              this.hashedFieldIndexes.add( fieldIndex );
          }
  
          // still null, so see if it already exists
          if ( fieldIndex == null ) {
              fieldIndex = findFieldIndex( index );
          }
  
          // doesn't exist so create it
          if ( fieldIndex == null ) {
              fieldIndex = new FieldIndex( index,
                                           fieldExtractor );
              this.hashedFieldIndexes.add( fieldIndex );
          }
  
          fieldIndex.increaseCounter();
  
          return fieldIndex;
      }