**Use case**

Is that column nullable or not 

**Describe the solution you'd like**

SELECT isNullable(NULL);

1 -- or true

**Describe alternatives you've considered**

```
WITH materialize(NULL) AS x
SELECT match(toColumnTypeName(x), 'Nullable') AS res

Query id: fa279bf2-38d5-41ae-89cb-187e588908db

┌─res─┐
│   1 │
└─────┘
```

**Additional context**

namespace DB
{
class FunctionFactory;
void registerFunctionIsNull(FunctionFactory & factory);
void registerFunctionIsNotNull(FunctionFactory & factory);
void registerFunctionCoalesce(FunctionFactory & factory);
void registerFunctionIfNull(FunctionFactory & factory);
void registerFunctionNullIf(FunctionFactory & factory);
void registerFunctionAssumeNotNull(FunctionFactory & factory);
void registerFunctionToNullable(FunctionFactory & factory);
void registerFunctionIsZeroOrNull(FunctionFactory & factory);
void registerFunctionsNull(FunctionFactory & factory)
{
    registerFunctionIsNull(factory);
    registerFunctionIsNotNull(factory);
    registerFunctionCoalesce(factory);
    registerFunctionIfNull(factory);
    registerFunctionNullIf(factory);
    registerFunctionAssumeNotNull(factory);
    registerFunctionToNullable(factory);
    registerFunctionIsZeroOrNull(factory);
}
}