presto-main/src/main/java/io/prestosql/metadata/FunctionArgumentDefinition.java/FunctionArgumentDefinition/equals
class FunctionArgumentDefinition:    @Override
    public boolean equals(Object o)
    {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        FunctionArgumentDefinition that = (FunctionArgumentDefinition) o;
        return nullable == that.nullable;
    }