Fix syntax error and incorrect use of MOPointer

[jeremyblalock]

The following issues were fixed:

• There was an erroneously-placed colon (:) on line 232, this has been removed
• When err is an MOPointer, err !== null always evaluates to true
  • Changing this to err.value() !== null we are able to fix the issue
  • Looked at this reference for MOPointer: https://github.com/logancollins/Mocha/blob/master/Mocha/Objects/MOPointer.h
• The error messages were no very helpful when logging err.description()
  • Instead, using err.value(), we are able to print out the actual MOPointer value with a helpful error message
  • err.value().description() would technically also work, but could cause problems if copy/pasted since we will need to ensure that err.value() is not null before calling

[mathieudutour]

Awesome, thanks!