Added Nulls getter to manipulate internal nulls on ColumnNullable (#107)

Author: dgrr

clickhouse/columns/nullable.cpp

@@ -23,6 +23,10 @@ ColumnRef ColumnNullable::Nested() const {
     return nested_;
 }
 
+ColumnRef ColumnNullable::Nulls() const {
+    return nulls_;
+}
+
 void ColumnNullable::Append(ColumnRef column) {
     if (auto col = column->As<ColumnNullable>()) {
         if (!col->nested_->Type()->IsEqual(nested_->Type())) {

clickhouse/columns/nullable.h

@@ -18,6 +18,9 @@ class ColumnNullable : public Column {
     /// Returns nested column.
     ColumnRef Nested() const;
 
+    /// Returns nulls column.
+    ColumnRef Nulls() const;
+
 public:
     /// Appends content of given column to the end of current one.
     void Append(ColumnRef column) override;