presto-main/src/main/java/io/prestosql/cost/ScalarStatsCalculator.java/ScalarStatsCalculator/visitCoalesceExpression
class ScalarStatsCalculator:        @Override
        protected SymbolStatsEstimate visitCoalesceExpression(CoalesceExpression node, Void context)
        {
            requireNonNull(node, "node is null");
            SymbolStatsEstimate result = null;
            for (Expression operand : node.getOperands()) {
                SymbolStatsEstimate operandEstimates = process(operand);
                if (result != null) {
                    result = estimateCoalesce(result, operandEstimates);
                }
                else {
                    result = operandEstimates;
                }
            }
            return requireNonNull(result, "result is null");
        }