@Override public int countMissing(){
  int count=0;
  for (int i=0; i < size(); i++) {
    if (MISSING_VALUE.equals(get(i))) {
      count++;
    }
  }
  return count;
}

@ Override public int countMissing ( ) { int count = 0 ; for ( int i = 0 ; i < size ( ) ; i ++ ) { if ( MISSING_VALUE . equals ( get ( i ) ) ) { count ++ ; } } return count ; }
returns the count of missing values in this column
