Program: 4280
Project: 4280
Buggy source:
/** 
 * Builds functions that map the fields from source CronDefinition to target
 * @param from - source CronDefinition
 * @param to - target CronDefinition
 */
private void buildMappings(CronDefinition from,CronDefinition to){
  Map<CronFieldName,FieldDefinition> sourceFieldDefinitions=Maps.newHashMap();
  Map<CronFieldName,FieldDefinition> destFieldDefinitions=Maps.newHashMap();
  for (  FieldDefinition fieldDefinition : from.getFieldDefinitions()) {
    sourceFieldDefinitions.put(fieldDefinition.getFieldName(),fieldDefinition);
  }
  for (  FieldDefinition fieldDefinition : to.getFieldDefinitions()) {
    destFieldDefinitions.put(fieldDefinition.getFieldName(),fieldDefinition);
  }
  boolean startedDestMapping=false;
  boolean startedSourceMapping=false;
  for (  CronFieldName name : CronFieldName.values()) {
    if (destFieldDefinitions.get(name) != null) {
      startedDestMapping=true;
    }
    if (sourceFieldDefinitions.get(name) != null) {
      startedSourceMapping=true;
    }
    if (startedDestMapping && destFieldDefinitions.get(name) == null) {
      break;
    }
    if (!startedSourceMapping && sourceFieldDefinitions.get(name) == null && destFieldDefinitions.get(name) != null) {
      mappings.put(name,returnOnZeroExpression(name));
    }
    if (startedSourceMapping && sourceFieldDefinitions.get(name) == null && destFieldDefinitions.get(name) != null) {
      mappings.put(name,returnAlwaysExpression(name));
    }
    if (sourceFieldDefinitions.get(name) != null && destFieldDefinitions.get(name) != null) {
      if (CronFieldName.DAY_OF_WEEK.equals(name)) {
        mappings.put(name,dayOfWeekMapping((DayOfWeekFieldDefinition)sourceFieldDefinitions.get(name),(DayOfWeekFieldDefinition)destFieldDefinitions.get(name)));
      }
 else {
        mappings.put(name,returnSameExpression());
      }
    }
  }
}

Fixed version (ground truth):
/** 
 * Builds functions that map the fields from source CronDefinition to target
 * @param from - source CronDefinition
 * @param to - target CronDefinition
 */
private void buildMappings(CronDefinition from,CronDefinition to){
  Map<CronFieldName,FieldDefinition> sourceFieldDefinitions=Maps.newHashMap();
  Map<CronFieldName,FieldDefinition> destFieldDefinitions=Maps.newHashMap();
  for (  FieldDefinition fieldDefinition : from.getFieldDefinitions()) {
    sourceFieldDefinitions.put(fieldDefinition.getFieldName(),fieldDefinition);
  }
  for (  FieldDefinition fieldDefinition : to.getFieldDefinitions()) {
    destFieldDefinitions.put(fieldDefinition.getFieldName(),fieldDefinition);
  }
  boolean startedDestMapping=false;
  boolean startedSourceMapping=false;
  for (  CronFieldName name : CronFieldName.values()) {
    if (destFieldDefinitions.get(name) != null) {
      startedDestMapping=true;
    }
    if (sourceFieldDefinitions.get(name) != null) {
      startedSourceMapping=true;
    }
    if (startedDestMapping && destFieldDefinitions.get(name) == null) {
      break;
    }
    if (!startedSourceMapping && sourceFieldDefinitions.get(name) == null && destFieldDefinitions.get(name) != null) {
      mappings.put(name,returnOnZeroExpression(name));
    }
    if (startedSourceMapping && sourceFieldDefinitions.get(name) == null && destFieldDefinitions.get(name) != null) {
      mappings.put(name,returnAlwaysExpression(name));
    }
    if (sourceFieldDefinitions.get(name) != null && destFieldDefinitions.get(name) != null) {
      if (CronFieldName.DAY_OF_WEEK.equals(name)) {
        mappings.put(name,dayOfWeekMapping((DayOfWeekFieldDefinition)sourceFieldDefinitions.get(name),(DayOfWeekFieldDefinition)destFieldDefinitions.get(name)));
      }
 else {
        if (CronFieldName.DAY_OF_MONTH.equals(name)) {
          mappings.put(name,dayOfMonthMapping(sourceFieldDefinitions.get(name),destFieldDefinitions.get(name)));
        }
 else {
          mappings.put(name,returnSameExpression());
        }
      }
    }
  }
}