Data set columns fix

Author: deepnetts

src/main/java/javax/visrec/ml/data/BasicDataSet.java

@@ -21,7 +21,7 @@ public class BasicDataSet<E> implements DataSet<E> {
  /**
  * List of data set columns. Each column provides info about it's name, type.
  */
- private List<Column> columns;
+ private List<Column> columns = new ArrayList();
 
  protected BasicDataSet() {
  items = new ArrayList<>();
@@ -62,7 +62,7 @@ public List<Column> getColumns() {
  }
 
  public void setColumnNames(String[] columnNames) {
- for(int i=0; i<columns.size(); i++) {
+ for(int i=0; i<columnNames.length; i++) {
  columns.get(i).setName(columnNames[i]);
  } 
  }