Program: 148401
Project: 148401
Buggy source:
public IStatus doAction(){
  try {
    XSDParticle particle=(XSDParticle)xsdPartle;
    if (particle == null) {
      ISelection selection=page.getTreeViewer().getSelection();
      particle=(XSDParticle)((IStructuredSelection)selection).getFirstElement();
    }
    XSDTerm term=particle.getTerm();
    XSDElementDeclaration decl=null;
    if (term instanceof XSDElementDeclaration) {
      decl=(XSDElementDeclaration)particle.getTerm();
    }
    if (particle.getContainer() == null) {
      return Status.CANCEL_STATUS;
    }
    XSDIdentityConstraintDefinition identify=null;
    XSDXPathDefinition keyPath=null;
    List<Object> keyInfo=Util.getKeyInfo(decl);
    if (keyInfo != null && keyInfo.size() > 0) {
      identify=(XSDIdentityConstraintDefinition)keyInfo.get(0);
      keyPath=(XSDXPathDefinition)keyInfo.get(1);
      identify.getFields().remove(keyPath);
      if (identify.getFields().size() == 0) {
        XSDElementDeclaration top=(XSDElementDeclaration)Util.getParent(decl);
        top.getIdentityConstraintDefinitions().remove(identify);
      }
    }
    if (!(particle.getContainer() instanceof XSDModelGroup))     throw new XtentisException("String_Node_Str" + particle.getContainer().getClass().getName());
    XSDModelGroup group=(XSDModelGroup)particle.getContainer();
    group.getContents().remove(particle);
    group.updateElement();
    xsdPartle=null;
    page.refresh();
    page.markDirty();
  }
 catch (  Exception e) {
    log.error(e.getStackTrace());
    MessageDialog.openError(page.getSite().getShell(),"String_Node_Str","String_Node_Str" + e.getLocalizedMessage());
    return Status.CANCEL_STATUS;
  }
  return Status.OK_STATUS;
}

Fixed version (ground truth):
public IStatus doAction(){
  try {
    XSDParticle particle=(XSDParticle)xsdPartle;
    if (particle == null) {
      ISelection selection=page.getTreeViewer().getSelection();
      particle=(XSDParticle)((IStructuredSelection)selection).getFirstElement();
    }
    XSDTerm term=particle.getTerm();
    XSDElementDeclaration decl=null;
    if (term instanceof XSDElementDeclaration) {
      decl=(XSDElementDeclaration)particle.getTerm();
    }
    if (particle.getContainer() == null) {
      return Status.CANCEL_STATUS;
    }
    XSDIdentityConstraintDefinition identify=null;
    XSDXPathDefinition keyPath=null;
    List<Object> keyInfo=Util.getKeyInfo(decl);
    if (keyInfo != null && keyInfo.size() > 0) {
      identify=(XSDIdentityConstraintDefinition)keyInfo.get(0);
      keyPath=(XSDXPathDefinition)keyInfo.get(1);
      identify.getFields().remove(keyPath);
      if (identify.getFields().size() == 0) {
        XSDElementDeclaration top=(XSDElementDeclaration)Util.getParent(decl);
        top.getIdentityConstraintDefinitions().remove(identify);
      }
    }
    if (!(particle.getContainer() instanceof XSDModelGroup))     throw new XtentisException("String_Node_Str" + particle.getContainer().getClass().getName());
    XSDModelGroup group=(XSDModelGroup)particle.getContainer();
    group.getContents().remove(particle);
    group.updateElement();
    xsdPartle=null;
    page.refresh();
    page.markDirty();
  }
 catch (  Exception e) {
    log.error(e.getMessage(),e);
    MessageDialog.openError(page.getSite().getShell(),"String_Node_Str","String_Node_Str" + e.getLocalizedMessage());
    return Status.CANCEL_STATUS;
  }
  return Status.OK_STATUS;
}