I am a beginner to Cloud Formation and I am using the yaml code below to try and update a pipeline in AWS. Upon committing the yaml code I get the following error

“[/Description] ‘null’ values are not allowed in templates (Service: AmazonCloudFormation; Status Code: 400; Error Code: ValidationError; Request ID: 265e178d-1e7a-4852-8008-f5848f51f4f8; Proxy: null)

I went back to my code and validated it with an online YAML validator and i get where the error is coming from but I am failing to fix the problem. I am getting this error:

Error: unknown tag !<!Ref> at line 27, column 34:
          InternetGatewayId: !Ref IGW
                                     ^
Line : undefined  undefined

My YAML code is below:

AWSTemplateFormatVersion: 2010-09-09
Description: Network layer for the cafe
Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.0.0.0/16
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
        - Key: Name
          Value: Cafe VPC

  IGW:
    Type: AWS::EC2::InternetGateway
    Properties:
      Tags:
        - Key: Name
          Value: Cafe IGW

  VPCtoIGWConnection:
    Type: AWS::EC2::VPCGatewayAttachment
    DependsOn:
      - IGW
      - VPC
    Properties:
      InternetGatewayId: !Ref IGW
      VpcId: !Ref VPC

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    DependsOn: VPC
    Properties:
      VpcId: !Ref VPC
      Tags:
        - Key: Name
          Value: Cafe Public Route Table

  PublicRoute:
    Type: AWS::EC2::Route
    DependsOn:
      - PublicRouteTable
      - VPCtoIGWConnection
    Properties:
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref IGW
      RouteTableId: !Ref PublicRouteTable

  PublicSubnet:
    Type: AWS::EC2::Subnet
    DependsOn: VPC
    Properties:
      VpcId: !Ref VPC
      MapPublicIpOnLaunch: true
      CidrBlock: 10.0.0.0/24
      AvailabilityZone: !Select
        - 0
        - !GetAZs
          Ref: AWS::Region
      Tags:
        - Key: Name
          Value: Cafe Public Subnet

  PublicRouteTableAssociation:
    Type: AWS::EC2::SubnetRouteTableAssociation
    DependsOn:
      - PublicRouteTable
      - PublicSubnet
    Properties:
      RouteTableId: !Ref PublicRouteTable
      SubnetId: !Ref PublicSubnet

I tried searching from AWS documentation but I don see where the error is coming from.