Program: 31690
Project: 31690
Buggy source:
/** 
 * Given an set of names (simple or fully-qualified) that are possibly within a type hierarchy, this function returns the base class from among them.
 * @param taxa the taxa (simple class names or labels)
 * @return The ClassInfo representing the base class among the taxa or <code>null</code> if it cannot be found
 */
public ClassInfo resolve(String... taxa){
  if (taxa.length > 0) {
    Set<ClassInfo> resolved=new HashSet<>();
    for (    String taxon : taxa) {
      ClassInfo taxonClassInfo=classInfo(taxon);
      if (taxonClassInfo == null) {
        continue;
      }
      if (taxonClassInfo.isInterface()) {
        taxonClassInfo=findSingleImplementor(taxon);
      }
 else       if (taxonClassInfo.isAbstract()) {
        taxonClassInfo=findFirstSingleConcreteClass(taxonClassInfo,taxonClassInfo.directSubclasses());
      }
      if (taxonClassInfo != null) {
        for (        ClassInfo found : resolved) {
          if (taxonClassInfo.isSubclassOf(found)) {
            resolved.remove(found);
            break;
          }
          if (found.isSubclassOf(taxonClassInfo)) {
            taxonClassInfo=null;
            break;
          }
        }
      }
      if (taxonClassInfo != null) {
        resolved.add(taxonClassInfo);
      }
    }
    if (resolved.size() > 1) {
      throw new AmbiguousBaseClassException(Arrays.toString(taxa));
    }
    if (resolved.iterator().hasNext()) {
      return resolved.iterator().next();
    }
  }
  return null;
}

Fixed version (ground truth):
/** 
 * Given an set of names (simple or fully-qualified) that are possibly within a type hierarchy, this function returns the base class from among them.
 * @param taxa the taxa (simple class names or labels)
 * @return The ClassInfo representing the base class among the taxa or <code>null</code> if it cannot be found
 */
public ClassInfo resolve(String... taxa){
  if (taxa.length > 0) {
    Set<ClassInfo> resolved=new HashSet<>();
    for (    String taxon : taxa) {
      LOGGER.debug("String_Node_Str" + taxon);
      ClassInfo taxonClassInfo=classInfo(taxon);
      if (taxonClassInfo == null) {
        LOGGER.debug("String_Node_Str");
        continue;
      }
      if (taxonClassInfo.isInterface()) {
        LOGGER.debug("String_Node_Str");
        taxonClassInfo=findSingleImplementor(taxon);
      }
 else       if (taxonClassInfo.isAbstract()) {
        LOGGER.debug("String_Node_Str");
        taxonClassInfo=findFirstSingleConcreteClass(taxonClassInfo,taxonClassInfo.directSubclasses());
      }
      if (taxonClassInfo != null) {
        LOGGER.debug("String_Node_Str" + taxonClassInfo + "String_Node_Str");
        for (        ClassInfo found : resolved) {
          if (taxonClassInfo.isSubclassOf(found)) {
            LOGGER.debug(taxonClassInfo + "String_Node_Str" + found+ "String_Node_Str");
            resolved.remove(found);
            break;
          }
          if (found.isSubclassOf(taxonClassInfo)) {
            LOGGER.debug(taxonClassInfo + "String_Node_Str" + found+ "String_Node_Str");
            taxonClassInfo=null;
            break;
          }
        }
      }
 else {
        LOGGER.debug("String_Node_Str");
      }
      if (taxonClassInfo != null) {
        LOGGER.debug(taxon + "String_Node_Str" + taxonClassInfo);
        resolved.add(taxonClassInfo);
      }
    }
    if (resolved.size() > 1) {
      throw new AmbiguousBaseClassException(Arrays.toString(taxa));
    }
    if (resolved.iterator().hasNext()) {
      return resolved.iterator().next();
    }
  }
  LOGGER.debug("String_Node_Str");
  return null;
}