ASP.Net Web API repository update error 500

My Web Api controller has a method UpdateAreathat is passed and updated value idin the body . The content is as follows:

[HttpPut("{id}")]
public async Task<IActionResult> UpdateArea(Guid id, [FromBody] AreaForUpdateDto areaForUpdateDto)
{
    // Check that the 'area' object parameter can be de-serialised to a AreaForUpdateDto.
    if (areaForUpdateDto == null)
    {
        _logger.LogError("AreasController.UpdateArea failed: Could not map area object parameter to a AreaForUpdateDto");

        // Return an error 400.
        return BadRequest();
    }

    // Ensure that the Area exists.
    var areaEntityFromRepo = _areaRepository.GetArea(id);

    // Map(source object (Dto), destination object (Entity))
    Mapper.Map(areaForUpdateDto, areaEntityFromRepo);
    _areaRepository.UpdateArea(areaEntityFromRepo);

    // Save the updated Area entity, added to the DbContext, to the SQL database.
    if (await _areaRepository.SaveChangesAsync())
    {
        var areaFromRepo = _areaRepository.GetArea(id);
        if (areaFromRepo == null)
            return NotFound();

        var area = Mapper.Map<AreaDto>(areaFromRepo);
        return Ok(area);
    }

    // The save has failed.
    _logger.LogWarning($"Updating Area {id} failed on save.");
    throw new Exception($"Updating Area {id} failed on save.");
}

This works fine until my app asks for an update, but the body of the request is the same as the existing data in the database. When this happens, _areaRepository.SaveChangesAsync()failure is returned error 500.

This happens if the user opens the Edit Details dialog, makes no changes, and then clicks the Edit button that sends the request.

I can validate on the client side, which is fine, but to my surprise this results in an error.

Can anyone explain why this fails and where should I correct it?