Add first sanity check

GerbilManagerWebAPI/Controllers/LittersController.cs

@@ -44,6 +44,14 @@ namespace GerbilManagerWebAPI.Controllers
         [HttpPost()]
         public ActionResult<LitterDto> CreateLitter(CreateLitterDto dto)
         {
+            //Sanity check if father is male and mother is female
+            var father = this.unitOfWork.GerbilRepository.GetByID(dto.Father ?? Guid.Empty);
+            var mother = this.unitOfWork.GerbilRepository.GetByID(dto.Mother ?? Guid.Empty);
+            if(father?.Gender == Gender.female || mother?.Gender == Gender.male)
+            {
+                return BadRequest($"The mothers gender is {mother?.Gender.ToString() ?? "unknown"} and the fathers {father?.Gender.ToString() ?? "unknown"}.");
+            }
+
             Litter litter = new Litter{
                 Id = Guid.NewGuid(),
                 Date = dto.Date,