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CreateColumnByType("Array(5)"), "Nullable(DateTime64)" or
"LowCardinality(Nullable(5))" crashed instead of reporting an
unsupported type. CreateColumnFromAst in columns/factory.cpp passed the
nested result straight to the ColumnArray and ColumnNullable
constructors, which call nested->Type() and dereference the null
pointer the factory returns for types it cannot create. Array and
Nullable now return nullptr like Tuple and Map already do, so Client
reports "unsupported column type", and LowCardinality(Nullable(T))
throws UnimplementedError like the generic LowCardinality branch.
This was referenced Oct 18, 2026
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CreateColumnByType("Array(5)"),"Nullable(DateTime64)"and"LowCardinality(Nullable(5))"segfault instead of reporting an unsupported type. A server can send these in a block header.CreateColumnFromAstincolumns/factory.cpppasses the nested result straight to theColumnArrayandColumnNullableconstructors. Both callnested->Type(), so they dereference the nullptr the factory returns for any type it can't build.Fix: Array and Nullable now return nullptr when the nested column is null, as Tuple and Map already do, so
Clientreports "unsupported column type".LowCardinality(Nullable(T))throwsUnimplementedError, matching the generic LowCardinality branch.Reproducer type strings:
Array(Null),Array(5),Array(DateTime64),Array(Time64),Nullable(5),Nullable(DateTime64),Array(Nullable(5)),LowCardinality(Nullable(5)).Test:
CreateColumnByType.UnsupportedNestedTypesegfaults on master and passes here. It also checks thatNullable(UInt8),Array(String),LowCardinality(Nullable(String))andArray(Nullable(DateTime64(3)))still round-trip their type names.This doesn't overlap #575; the two merge cleanly.