```
_fontAtlas->getLetterDefinitionForChar(theChar, _lettersInfo[spriteIndex].def);
```
if above code fails, _lettersInfo[spriteIndex].def.validDefinition will be uninitialized value.
I found that below code also can fix the problem
```
    if (!_fontAtlas->getLetterDefinitionForChar(theChar, _lettersInfo[spriteIndex].def))
        _lettersInfo[spriteIndex].def.validDefinition = false;
```