AWS Cloud Frormation Template contains errors.: Template format error: YAML not well-formed. (line 7, column 1)

Question

While am validating below template in cloudformation designer section, am getting error: Template contains errors.: Template format error: YAML not well-formed. (line 7, column 1).... Could anyone pls correct the syntax at line 7 column 1.

  1 AWSTemplateFormatVersion: 2010-09-09
  2 Resources:
  3  Ec2Instance:
  4    Type: AWS::EC2::Instance
  5    Properties:
  6     Securitygroups:
  7           -!Ref InstanceSecurityGroup
  8         KeyName: testkey
  9         ImageId: ''
 10  InstanceSecurityGroup:
 11     Type: AWS::Ec2::SecurityGroup
 12         Properties:
 13          GroupDescription: Enable SSH access via port 22
 14          SecurityGroupIngress:
 15           - IpProtocol: tcp
 16             FromPort: '22'
 17                 ToPort: '22'
 18                 CidrIp: 0.0.0.0/0