v2.0.1
1. prefer exception message 2. fix Null Coalescing Operator in php 5.6 3. use `$array[]` instead of `array_push` ( https://stackoverflow.com/a/559859 ) 4. fix miss or wrong check in 'piece layers', 'path'
1. prefer exception message 2. fix Null Coalescing Operator in php 5.6 3. use `$array[]` instead of `array_push` ( https://stackoverflow.com/a/559859 ) 4. fix miss or wrong check in 'piece layers', 'path'