diff --git a/dbms/src/Columns/ColumnArray.cpp b/dbms/src/Columns/ColumnArray.cpp
index 73ea0c2910b..b4382755ba3 100644
--- a/dbms/src/Columns/ColumnArray.cpp
+++ b/dbms/src/Columns/ColumnArray.cpp
@@ -809,12 +809,12 @@ ColumnPtr ColumnArray::replicateString(const Offsets & replicate_offsets) const
 
     for (size_t i = 0; i < col_size; ++i)
     {
-        /// How much to replicate the array.
+        /// How many times to replicate the array.
         size_t size_to_replicate = replicate_offsets[i] - prev_replicate_offset;
-        /// The number of rows in the array.
+        /// The number of strings in the array.
         size_t value_size = src_offsets[i] - prev_src_offset;
-        /// Number of characters in rows of the array, including zero/null bytes.
-        size_t sum_chars_size = value_size == 0 ? 0 : (src_string_offsets[prev_src_offset + value_size - 1] - prev_src_string_offset);
+        /// Number of characters in strings of the array, including zero bytes.
+        size_t sum_chars_size = src_string_offsets[prev_src_offset + value_size - 1] - prev_src_string_offset;  /// -1th index is Ok, see PaddedPODArray.
 
         for (size_t j = 0; j < size_to_replicate; ++j)
         {
@@ -824,7 +824,7 @@ ColumnPtr ColumnArray::replicateString(const Offsets & replicate_offsets) const
             size_t prev_src_string_offset_local = prev_src_string_offset;
             for (size_t k = 0; k < value_size; ++k)
             {
-                /// Size of one string.
+                /// Size of single string.
                 size_t chars_size = src_string_offsets[k + prev_src_offset] - prev_src_string_offset_local;
 
                 current_res_string_offset += chars_size;
diff --git a/dbms/src/Columns/ColumnString.cpp b/dbms/src/Columns/ColumnString.cpp
index 1443283783a..78d2f3ce045 100644
--- a/dbms/src/Columns/ColumnString.cpp
+++ b/dbms/src/Columns/ColumnString.cpp
@@ -88,7 +88,7 @@ void ColumnString::insertRangeFrom(const IColumn & src, size_t start, size_t len
     else
     {
         size_t old_size = offsets.size();
-        size_t prev_max_offset = old_size ? offsets.back() : 0;
+        size_t prev_max_offset = offsets.back();    /// -1th index is Ok, see PaddedPODArray
         offsets.resize(old_size + length);
 
         for (size_t i = 0; i < length; ++i)
diff --git a/dbms/src/Functions/FunctionArrayMapped.h b/dbms/src/Functions/FunctionArrayMapped.h
index bb9b0ad3c74..dc25b228ce9 100644
--- a/dbms/src/Functions/FunctionArrayMapped.h
+++ b/dbms/src/Functions/FunctionArrayMapped.h
@@ -161,6 +161,10 @@ public:
 
             const auto * column_function = typeid_cast<const ColumnFunction *>(column_with_type_and_name.column.get());
 
+            if (!column_function)
+                throw Exception("First argument for function " + getName() + " must be a function.",
+                    ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
+
             ColumnPtr offsets_column;
 
             ColumnPtr column_first_array_ptr;
diff --git a/dbms/src/Functions/FunctionsBitmap.h b/dbms/src/Functions/FunctionsBitmap.h
index 2fefaed9f2b..88c17feeb5c 100644
--- a/dbms/src/Functions/FunctionsBitmap.h
+++ b/dbms/src/Functions/FunctionsBitmap.h
@@ -5,7 +5,6 @@
 #include <Columns/ColumnAggregateFunction.h>
 #include <Columns/ColumnArray.h>
 #include <Columns/ColumnConst.h>
-#include <Columns/ColumnFunction.h>
 #include <Columns/ColumnVector.h>
 #include <DataTypes/DataTypeAggregateFunction.h>
 #include <DataTypes/DataTypeArray.h>
@@ -14,6 +13,7 @@
 #include <Functions/IFunction.h>
 #include <Common/typeid_cast.h>
 
+
 namespace DB
 {
 namespace ErrorCodes