Amazon web services – Terraform AWS: host for provisioner cannot be empty

I keep getting error "host for provisioner cannot be empty"

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

# Configure the AWS Provider
provider "aws" {
  region  = var.region
  profile = "whatsnxt"
}

resource "tls_private_key" "rsa_4096" {
  algorithm = "RSA"
  rsa_bits  = 4096
}

#  create key pair for connecting to EC2 via SSH
resource "aws_key_pair" "key_pair" {
  key_name   = var.key_pair_name
  public_key = tls_private_key.rsa_4096.public_key_openssh
}

resource "local_file" "private_key" {
  content  = tls_private_key.rsa_4096.private_key_openssh
  filename = pathexpand("~/.ssh/${var.private_key}")

  provisioner "local-exec" {
    command = "chmod 400 ${self.filename}"
  }
}

# update docker image when var.image_version changes
resource "null_resource" "image_updater" {
  depends_on = [ null_resource.node_provisioner, module.ec2_instance ]
  triggers = {
    image_version = var.image_version
  }

  connection {
    host = module.ec2_instance.public_ip
    user = "ec2-user"
    type = "ssh"
    private_key = local_file.private_key.content
  }

  provisioner "file" {
    source      = "run-image.sh"
    destination = "run-image.sh"
  }
  provisioner "file" {
    source      = "../.env"
    destination = ".env"
  }  
  provisioner "remote-exec" {
    inline = [
      "chmod +x run-image.sh",
      "./run-image.sh ${var.image_version}"
    ]
  }
}

module "ec2_instance" {
  source  = "terraform-aws-modules/ec2-instance/aws"

  ami                    = var.ami
  name                   = var.instance_name
  instance_type          = var.instance_type
  key_name               = aws_key_pair.key_pair.key_name
  monitoring             = true
  subnet_id              = aws_subnet.blog_public_subnet.id
  vpc_security_group_ids = [aws_security_group.blogSG.id]
  user_data = <<-EOF
                    #!/bin/bash -xe
                    sudo yum update -y
                    sudo yum install docker -y
                    sudo systemctl enable docker.service
                    sudo systemctl start docker.service
                    sleep 15
                  EOF  

  tags = {
    Terraform   = "true"
    Environment = "dev"
    Name        = var.instance_name
  }

}

resource "null_resource" "node_provisioner" {
  depends_on = [ module.ec2_instance ]
  
  triggers = {
    instance_id = module.ec2_instance.id
  }

  connection {
    host = module.ec2_instance.public_ip
    user = "ec2-user"
    type = "ssh"
    private_key = local_file.private_key.content
  }

  provisioner "file" {
    source      = ".credentials"
    destination = "credentials"
  }

  provisioner "remote-exec" {
    inline = [
      "mkdir -p .aws",
      "mv credentials .aws/credentials"
    ]
  }

}
# resource "aws_default_vpc" "default" {
#   tags = {
#     Name = "Default blog webserver VPC"
#   }
# }

resource "aws_vpc" "blog_vpc" {
  cidr_block = "10.0.0.0/16"

  tags = {
    Name = "Custom Blog VPC"
  }
}

resource "aws_subnet" "blog_public_subnet" {
  vpc_id            = aws_vpc.blog_vpc.id
  cidr_block        = "10.0.1.0/24"
  availability_zone = var.availability_zone

  tags = {
    Name = "Blog Public Subnet"
  }
}

resource "aws_subnet" "blog_private_subnet" {
  vpc_id            = aws_vpc.blog_vpc.id
  cidr_block        = "10.0.2.0/24"
  availability_zone = var.availability_zone

  tags = {
    Name = "Blog Private Subnet"
  }
}

resource "aws_internet_gateway" "blog_ig" {
  vpc_id = aws_vpc.blog_vpc.id

  tags = {
    Name = "Blog Internet Gateway"
  }
}

resource "aws_route_table" "public_rt" {
  vpc_id = aws_vpc.blog_vpc.id

  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.blog_ig.id
  }

  route {
    ipv6_cidr_block = "::/0"
    gateway_id      = aws_internet_gateway.blog_ig.id
  }

  tags = {
    Name = "Public Route Table"
  }
}

resource "aws_route_table_association" "public_1_rt_a" {
  subnet_id      = aws_subnet.blog_public_subnet.id
  route_table_id = aws_route_table.public_rt.id
}

resource "aws_security_group" "blogSG" {
  name        = "Blog Webserver SG"
  description = "Blog Webserver Security Group"
  vpc_id      = aws_vpc.blog_vpc.id

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    from_port   = 22
    to_port     = 22
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }

}