Null value for number_missing_values #20

Activity

1. rohansen856 commented on Nov 16, 2025

   

   rohansen856

   on Nov 16, 2025

   More actions

   Hi @ArlindKadra the getNumberOfMissingValues() could return null when the OpenML API returns empty XML elements like <oml:NumberOfMissingValues />. The problem occurred because: XStream XML parsing library had no converter for empty Integer elements, only for empty Double elements via EmptyDoubleConverter

   I propose a fix with the following solution:

   1. Create EmptyIntegerConverter.java in apiconnector/src/main/java/org/openml/apiconnector/xstream:

     package org.openml.apiconnector.xstream;
   
     import org.apache.commons.lang3.StringUtils;
     import com.thoughtworks.xstream.converters.basic.IntConverter;
   
     public class EmptyIntegerConverter extends IntConverter {
         public boolean canConvert(Class type) {
             return type.equals(Integer.class);
         }
   
         public Object fromString(String str) {
             if (StringUtils.isEmpty(str)) {
                 return null;
             }
             return Integer.valueOf(str);
         }
     }

   2. Modify: XstreamXmlMapping.java (line 105-106):

     xstream.registerConverter(new EmptyDoubleConverter());
     xstream.registerConverter(new EmptyIntegerConverter()); // Added this line

   These changes ensure that:

   • When the API returns <oml:NumberOfMissingValues />, XStream now properly converts it to null instead of causing a parsing exception
   • The user's code that checks feature.getNumberOfMissingValues() != null && feature.getNumberOfMissingValues() instanceof Integer now works correctly
   • Empty XML elements for any Integer field in DataFeature are now handled gracefully

   The fix ensures backward compatibility while resolving the null pointer issue.

   I would like to raise a PR with the approach to solve this issue. Thannks!