RestSharp: RestRequest post fails when using AddBody with string. This worked fine in 107.3.0.

This piece of code works just fine using restsharp v107.3.0 but failes when using 108.0.1

public async Task PostTest()
        {
            var calcId = await AddCalculationSetup();

            string paramValue = "InvalidValue";

            // Set a parameter with an invalid value
            var request = new RestRequest($"{url}/CalculationSetups/{calcId}/Parameters/InheritsFromCalcSetup").
                              AddBody(paramValue);
            var response = await restClient.ExecutePostAsync(request); 
            Assert.AreEqual(HttpStatusCode.Created, response.StatusCode, response.Content);
           . . .

The controller handler involved looks like this, but doesnt get called when using restclient v108, as stated before v107 works fine.

. . .
        /// <summary>
        /// Set a value for a parameter
        /// </summary>
        /// <param name="projectIdentifier">identifier of the project</param>
        /// <param name="itemIdentifier">identifier of the parameterized collection item</param>
        /// <param name="parameterIdentifier">identifier of the parammeter</param>
        /// <param name="value">value for the param</param>
        [HttpPost]
        [SwaggerOperation("Set a value for a parameter")]
        [Route("{parameterIdentifier}")]
        [SwaggerResponse(StatusCodes.Status201Created)]
        [SwaggerResponse(StatusCodes.Status404NotFound, Type = typeof(string))]
        [SwaggerResponse(StatusCodes.Status400BadRequest)]
        public virtual IActionResult Post(string projectIdentifier, string itemIdentifier, string parameterIdentifier, [FromBody] object value)
        { . . . }

The Assert in the unit test statement fails, and error returned is:

 PostTest
   Source: ValueSetTest.cs line 30
   Duration: 200 ms

  Message: 
Assert.AreEqual failed. Expected:<Created>. Actual:<BadRequest>. {
  "type": "https://tools.ietf.org/html/rfc7231#section-6.5.1",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "traceId": "00-4fc8ce2dfbaa969137ff4f9482017569-1090e9c87770ee73-00",
  "errors": {
    "$": [
      "'I' is an invalid start of a value. Path: $ | LineNumber: 0 | BytePositionInLine: 0."
    ],
    "value": [
      "The value field is required."
    ]
  }
}

  Stack Trace: 
ValueSetTest.PostTest() line 40
ThreadOperations.ExecuteWithAbortSafety(Action action)

• Thx, Hans