WebRequestPSCmdlet.Common.cs

....
        #region Method

        /// <summary>
        /// gets or sets the Method property
        /// </summary>
        [Parameter(parametersetname="StandardMethod")]
        [Parameter(parametersetname="StandardMethodNoProxy")]
        public virtual WebRequestMethod Method
        {
            get { return _method; }
            set { _method = value; }
        }
        private WebRequestMethod _method = WebRequestMethod.Default;

        /// <summary>
        /// gets or sets the CustomMethod property
        /// </summary>
        [Parameter(parametersetname="CustomMethod")]
        [Parameter(parametersetname="CustomMethodNoProxy")]
        [Alias("CM")]
        [ValidateNotNullOrEmpty]
        public virtual string CustomMethod
        {
            get { return _customMethod; }
            set { _customMethod = value; }
        }
        private string _customMethod;

        #endregion

        #region NoProxy

        /// <summary>
        /// gets or sets the NoProxy property
        /// </summary>
        [Parameter(mandatory=true,parametersetname="CustomMethodNoProxy")]
        [Parameter(mandatory=true,parametersetname="StandardMethodNoProxy")]
        public virtual SwitchParameter NoProxy { get; set; }

        #endregion

        #region Proxy

        /// <summary>
        /// gets or sets the Proxy property
        /// </summary>
        [Parameter(parametersetname="StandardMethod")]
        [Parameter(parametersetname="CustomMethod")]
        public virtual Uri Proxy { get; set; }

        /// <summary>
        /// gets or sets the ProxyCredential property
        /// </summary>
        [Parameter(parametersetname="StandardMethod")]
        [Parameter(parametersetname="CustomMethod")]
        [Credential]
        public virtual PSCredential ProxyCredential { get; set; }

        /// <summary>
        /// gets or sets the ProxyUseDefaultCredentials property
        /// </summary>
        [Parameter(parametersetname="StandardMethod")]
        [Parameter(parametersetname="CustomMethod")]
        public virtual SwitchParameter ProxyUseDefaultCredentials { get; set; }

        #endregion
....

WebRequestPSCmdlet.CoreClr.cs

....
        internal virtual HttpRequestMessage GetRequest(Uri uri)
        {
            Uri requestUri = PrepareUri(uri);
            HttpMethod httpMethod = null;

            switch (ParameterSetName)
            {
                case "StandardMethodNoProxy":
                goto case "StandardMethod";
                case "StandardMethod":
                    // set the method if the parameter was provided
                    httpMethod = GetHttpMethod(Method);
                    break;
                case "CustomMethodNoProxy":
                goto case "CustomMethod";
                case "CustomMethod":
                    if (!string.IsNullOrEmpty(CustomMethod))
                    {
                        // set the method if the parameter was provided
                        httpMethod = new HttpMethod(CustomMethod.ToString().ToUpperInvariant());
                    }
                    break;
            }