@Override
  public ColumnCount getColumnHint() {
    return null;
  }
Used by matcher and scan/get to get a hint of the next column to seek to after checkColumn()
returns SKIP. Returns the next interesting column we want, or NULL there is none (wildcard
scanner).
@return The column count.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/querymatcher/ScanWildcardColumnTracker.java