Strange CGPDFBoolean Stuff

CGPDFBoolean.m

// Simple object, not an array or dictionary.
- (void)pushObject:(NSObject *)object withKey:(NSString *)key {
    NSObject *last = [stack lastObject];
    if ([last isKindOfClass:[NSMutableDictionary class]]) {
        NSMutableDictionary *dictionary = (NSMutableDictionary *)last;
        // Exception raised here.
        // *** setObjectForKey: object cannot be nil (key: BaseFont)
        [dictionary setObject:object forKey:key];
    } else if ([last isKindOfClass:[NSMutableArray class]]) {
        NSMutableArray *array = (NSMutableArray *)last;
        [array addObject:object];
    }
}

- (void)scanPDFNode:(const char *)cStringKey context:(MMPDFScannerContext *)context object:(CGPDFObjectRef)object dictionary:(CGPDFDictionaryRef)dictionaryRef isArray:(BOOL)isArray {
    NSString *key = [NSString stringWithUTF8String:cStringKey];
    
    CGPDFObjectType type = CGPDFObjectGetType(object);
    switch (type) {
        case kCGPDFObjectTypeNull:
            [self pushObject:[NSNull null] withKey:key];
            break;
        case kCGPDFObjectTypeBoolean:
        {
            CGPDFBoolean pdfBoolean;
            if (CGPDFObjectGetValue(object, type, &pdfBoolean)) {
                // Exception raised inside -pushObject:withKey: from this path.
                [self pushObject:[NSNumber numberWithBool:(BOOL)pdfBoolean] withKey:key];
            }
            break;
        }
...

All of this happening inside a CGPDFDictionaryApplyFunction applier function.