apex classes vison controller error

Use Below Code

public class VisionController {
    // You can upload the 'einstein_platform.pem' into your Salesforce org as 'File' sObject and read it as below
    public String getAccessToken() {
        // Ignore the File upload part and "jwt.pkcs" if you used a Salesforce certificate to sign up
        // for an Einstein Platform account
        ContentVersion base64Content = [SELECT Title, VersionData FROM ContentVersion where Title='einstein_platform' OR  Title='predictive_services' ORDER BY Title LIMIT 1];
        String keyContents = base64Content.VersionData.tostring();
        keyContents = keyContents.replace('-----BEGIN RSA PRIVATE KEY-----', '');
        keyContents = keyContents.replace('-----END RSA PRIVATE KEY-----', '');
        keyContents = keyContents.replace('\n', '');
        // Get a new token
        JWT jwt = new JWT('RS256');
        // jwt.cert = 'JWTCert'; // Uncomment this if you used a Salesforce certificate to sign up for an Einstein Platform account
        jwt.pkcs8 = keyContents; // Comment this if you are using jwt.cert
        jwt.iss = 'developer.force.com';
        jwt.sub = 'john.bryant@halliburton.com';
        jwt.aud = 'https://api.metamind.io/v1/oauth2/token';
        jwt.exp = '3600';
        String access_token = JWTBearerFlow.getAccessToken('https://api.metamind.io/v1/oauth2/token', jwt);
        return access_token;   
    }
    public List<Vision.Prediction> getCallVisionUrl() {
        // Get a new token
        String access_token = getAccessToken();
        // Make a prediction using URL to a file
        return Vision.predictUrl('http://metamind.io/images/generalimage.jpg',access_token,'GeneralImageClassifier');
    }
    public List<Vision.Prediction> getCallVisionContent() {
        // Get a new token
        String access_token = getAccessToken();
        // Make a prediction for an image stored in Salesforce
        // by passing the file as blob which is then converted to base64 string
        ContentVersion content = [SELECT Title,VersionData FROM ContentVersion where Id = '06841000000LkfCAAS' LIMIT 1];
        return Vision.predictBlob(content.VersionData, access_token, 'GeneralImageClassifier');
    }
}