presto-spi/src/main/java/io/prestosql/spi/block/VariableWidthBlockBuilder.java/VariableWidthBlockBuilder/initializeCapacity
class VariableWidthBlockBuilder:    private void initializeCapacity()
    {
        if (positions != 0 || currentEntrySize != 0) {
            throw new IllegalStateException(getClass().getSimpleName() + " was used before initialization");
        }
        initialized = true;
        valueIsNull = new boolean[initialEntryCount];
        offsets = new int[initialEntryCount + 1];
        sliceOutput = new DynamicSliceOutput(initialSliceOutputSize);
        updateArraysDataSize();
    }