address comments

velox/buffer/Buffer.cpp

@@ -61,9 +61,7 @@ BufferPtr Buffer::slice<bool>(
     size_t offset,
     size_t length,
     memory::MemoryPool* pool) {
-  if (!buffer) {
-    return nullptr;
-  }
+  VELOX_CHECK_NOT_NULL(buffer, "Buffer must not be null.");
 
   if (offset % 8 == 0) {
     return sliceBufferZeroCopy(

velox/buffer/Buffer.h

@@ -181,8 +181,7 @@ class Buffer {
   /// Otherwise return a BufferView into the original buffer (with shared
   /// ownership of original buffer).
   ///
-  /// @param buffer A pointer to the buffer to be sliced. If this is null, the
-  /// function returns a null pointer.
+  /// @param buffer A pointer to the buffer to be sliced. Must not be null.
   /// @param offset The element position in the buffer where the slice begins.
   /// Must be less or equal than the buffer size.
   /// @param length The number of elements to include in the slice. Must be
@@ -195,9 +194,7 @@ class Buffer {
       size_t offset,
       size_t length,
       memory::MemoryPool* pool) {
-    if (!buffer) {
-      return nullptr;
-    }
+    VELOX_CHECK_NOT_NULL(buffer, "Buffer must not be null.");
     return sliceBufferZeroCopy(
         sizeof(T), is_pod_like_v<T>, buffer, offset, length);
   }
@@ -698,5 +695,6 @@ class BufferView : public Buffer {
 
   Releaser const releaser_;
 };
+
 } // namespace velox
 } // namespace facebook

velox/buffer/tests/BufferTest.cpp

@@ -466,6 +466,9 @@ TEST_F(BufferTest, sliceBigintBuffer) {
   VELOX_ASSERT_THROW(
       Buffer::slice<int64_t>(bufferPtr, 5, 6, pool_.get()),
       "Length must be less than or equal to 5.");
+  VELOX_ASSERT_THROW(
+      Buffer::slice<int64_t>(nullptr, 5, 6, pool_.get()),
+      "Buffer must not be null.");
 }
 
 TEST_F(BufferTest, sliceBooleanBuffer) {

velox/vector/BaseVector.h

@@ -883,7 +883,7 @@ class BaseVector {
   }
 
   BufferPtr sliceNulls(vector_size_t offset, vector_size_t length) const {
-    return Buffer::slice<bool>(nulls_, offset, length, pool_);
+    return nulls_ ? Buffer::slice<bool>(nulls_, offset, length, pool_) : nulls_;
   }
 
   TypePtr type_;

velox/vector/ComplexVector.cpp

@@ -1186,8 +1186,10 @@ VectorPtr ArrayVector::slice(vector_size_t offset, vector_size_t length) const {
       type_,
       sliceNulls(offset, length),
       length,
-      Buffer::slice<vector_size_t>(offsets_, offset, length, pool_),
-      Buffer::slice<vector_size_t>(sizes_, offset, length, pool_),
+      offsets_ ? Buffer::slice<vector_size_t>(offsets_, offset, length, pool_)
+               : offsets_,
+      sizes_ ? Buffer::slice<vector_size_t>(sizes_, offset, length, pool_)
+             : sizes_,
       elements_);
 }
 
@@ -1485,8 +1487,10 @@ VectorPtr MapVector::slice(vector_size_t offset, vector_size_t length) const {
       type_,
       sliceNulls(offset, length),
       length,
-      Buffer::slice<vector_size_t>(offsets_, offset, length, pool_),
-      Buffer::slice<vector_size_t>(sizes_, offset, length, pool_),
+      offsets_ ? Buffer::slice<vector_size_t>(offsets_, offset, length, pool_)
+               : offsets_,
+      sizes_ ? Buffer::slice<vector_size_t>(sizes_, offset, length, pool_)
+             : sizes_,
       keys_,
       values_);
 }

velox/vector/DictionaryVector-inl.h

@@ -185,7 +185,9 @@ VectorPtr DictionaryVector<T>::slice(vector_size_t offset, vector_size_t length)
       this->sliceNulls(offset, length),
       length,
       valueVector(),
-      Buffer::slice<vector_size_t>(indices_, offset, length, this->pool_));
+      indices_
+          ? Buffer::slice<vector_size_t>(indices_, offset, length, this->pool_)
+          : indices_);
 }
 
 template <typename T>

velox/vector/FlatVector-inl.h

@@ -423,7 +423,8 @@ VectorPtr FlatVector<T>::slice(vector_size_t offset, vector_size_t length)
       this->type_,
       this->sliceNulls(offset, length),
       length,
-      Buffer::slice<T>(values_, offset, length, this->pool_),
+      values_ ? Buffer::slice<T>(values_, offset, length, this->pool_)
+              : values_,
       std::vector<BufferPtr>(stringBuffers_));
 }