Handle NULLs in default metrics

Author: p-senichenkov

src/core/config/custom_metric/custom_metric.h

@@ -85,6 +85,9 @@ class DefaultCustomMetric : public ICustomMetric {
 public:
     double Dist(model::Type const* type, std::byte const* first,
                 std::byte const* second) const override {
+        if (!first || !second) {
+            return 0;
+        }
         return ConvertType(type)->Dist(first, second);
     }
 };

src/core/config/custom_metric/custom_vector_metric.h

@@ -65,7 +65,9 @@ class DefaultCustomVectorMetric : public ICustomVectorMetric {
 
         double result = 0;
         for (std::size_t i = 0; i < types.size(); ++i) {
-            result += std::pow(ConvertType(types[i])->Dist(first[i], second[i]), 2);
+            if (first[i] && second[i]) {
+                result += std::pow(ConvertType(types[i])->Dist(first[i], second[i]), 2);
+            }
         }
         return std::sqrt(result);
     }