Both methods used to optionally return null if passed a
second argument. This second argument was removed entirely and the
method always returns a RowDimension or ColumnDimension respectively
(possibly creating it if needed).
This make the API more predictable and easier to do static analysis
with tools such as PHPStan.
If you relied on that second parameter, you should instead use the
`Worksheet::getRowDimensions()` or `Worksheet::getColumnDimensions()` and
check for existence yourself before calling the getters.
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