code: private static Expression tryTransformIsToCompareIdentity(MethodCallExpression call) {
          MethodNode methodTarget = call.getMethodTarget();
          if (methodTarget instanceof ExtensionMethodNode && "is".equals(methodTarget.getName()) && methodTarget.getParameters().length==1) {
             methodTarget = ((ExtensionMethodNode) methodTarget).getExtensionMethodNode();
              ClassNode owner = methodTarget.getDeclaringClass();
              if (DGM_CLASSNODE.equals(owner)) {
                  Expression args = call.getArguments();
                  if (args instanceof ArgumentListExpression) {
                      ArgumentListExpression arguments = (ArgumentListExpression) args;
                      List<Expression> exprs = arguments.getExpressions();
                      if (exprs.size() == 1) {
                          CompareIdentityExpression cid = new CompareIdentityExpression(call.getObjectExpression(), exprs.get(0));
                          cid.setSourcePosition(call);
                          return cid;
                      }
                  }
              }
          }
          return null;
      }
docs: Identifies a method call expression on {@link DefaultGroovyMethods#is(Object, Object)} and if recognized, transforms it into a {@link CompareIdentityExpression}.
  @param call a method call to be transformed
  @return null if the method call is not DGM#is, or {@link CompareIdentityExpression}