Why do i need to pass in the generics here?

using GitManager.Domain.Models;
using GitManager.GitCLI.Commands.Parsing;

namespace GitManager.GitCLI.Commands
{
    public record GitPullBranchCommandInput : IGitCommandInput
    {
        public string LocalPath { get; }
        /// <summary>
        /// When not specified, the current local checked out branch will be pulled.
        /// </summary>
        public string? Branch { get; }

        public GitPullBranchCommandInput(string localPath, string? branch = null)
        {
            LocalPath = localPath;
            Branch = branch;
        }
    }
    public class GitPullBranchCommand : IGitCommand<string, GitPullBranchCommandInput>
    {
        private readonly IGitCommandStrategy _gitCommandStrategy;

        public GitPullBranchCommand(IGitCommandStrategy gitCommandStrategy)
        {
            _gitCommandStrategy = gitCommandStrategy;
        }

        public async Task<string> ExecuteAsync(GitPullBranchCommandInput input)
        {
            //var command = "branch --list --all";
            var command = "pull";
            var result = await _gitCommandStrategy.ExecuteAsync(command, input.LocalPath);

            return result;
        }
    }
}

Branch branch = await gitHandler.ExecuteAsync(new GitPullBranchCommandInput(""));