public Builder oldModel(ValidatedResult<Model> oldModel) {
            this.oldModel = oldModel.getResult()
                    .orElseThrow(() -> new IllegalArgumentException("No old model present in ValidatedResult"));
            this.oldModelEvents = oldModel.getValidationEvents();
            return this;
        }
Sets the old model to compare against along with the validation
events encountered while loading the model.

@param oldModel Old version of a model with events.
@return Returns the builder.
smithy-diff/src/main/java/software/amazon/smithy/diff/ModelDiff.java