Issue #1024: Add validations

Author: Serg046

src/BenchmarkDotNet/Reports/Summary.cs

@@ -76,11 +76,14 @@ private static BenchmarkCase GetFastestBenchmarkCase(ImmutableArray<BenchmarkRep
             if (reports.Any() && reports.All(r => r.BenchmarkCase.Config.AutomaticBaselineMode == AutomaticBaselineMode.Fastest))
             {
                 var fastestReport = reports.First();
-                foreach (var report in reports.Skip(1))
+                if (fastestReport.ResultStatistics != null)
                 {
-                    if (report.ResultStatistics.Mean < fastestReport.ResultStatistics.Mean)
+                    foreach (var report in reports.Skip(1).Where(r => r.ResultStatistics != null))
                     {
-                        fastestReport = report;
+                        if (report.ResultStatistics.Mean < fastestReport.ResultStatistics.Mean)
+                        {
+                            fastestReport = report;
+                        }
                     }
                 }
                 return fastestReport.BenchmarkCase;

src/BenchmarkDotNet/Validators/BaselineValidator.cs

@@ -14,6 +14,17 @@ private BaselineValidator() { }
 
         public IEnumerable<ValidationError> Validate(ValidationParameters input)
         {
+            if (input.Config.AutomaticBaselineMode != Configs.AutomaticBaselineMode.None)
+            {
+                foreach (var benchmark in input.Benchmarks)
+                {
+                    if (benchmark.Descriptor.Baseline || benchmark.Job.Meta.Baseline)
+                    {
+                        yield return new ValidationError(TreatsWarningsAsErrors, "You cannot use both pre-configured and automatic baseline configuration", benchmark);
+                    }
+                }
+            }
+
             var allBenchmarks = input.Benchmarks.ToImmutableArray();
             var orderProvider = input.Config.Orderer;