@Override
	public FieldList addField(Integer fieldID) {
		if (fieldID == null) {
			throw new IllegalArgumentException("Field ID must not be null.");
		}
		
		if (size() == 0) {
			return new FieldList(fieldID);
		} else {
			ArrayList<Integer> list = new ArrayList<Integer>(size() + 1);
			list.addAll(this.collection);
			list.add(fieldID);
			return new FieldList(Collections.unmodifiableList(list));
		}
	}
@ Override public FieldList addField ( Integer fieldID ) { if ( fieldID == null ) { throw new IllegalArgumentException ( "Field ID must not be null." ) ; } if ( size ( ) == 0 ) { return new FieldList ( fieldID ) ; } else { ArrayList < Integer > list = new ArrayList < Integer > ( size ( ) + 1 ) ; list . addAll ( this . collection ) ; list . add ( fieldID ) ; return new FieldList ( Collections . unmodifiableList ( list ) ) ; } }
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