iOS 字符串是否为空判断方法

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可以写个分类来处理

- (BOOL)blankString{
    if (![self isKindOfClass:[NSString class]] ){
        return  YES;
    }
    if ([self isEqual:[NSNull null]]){
        return  YES;
    }
    if (self == NULL || [self isEqual:nil] || [self isEqual:Nil] || self == nil){
        return  YES;
    }
    if([self isEqualToString:@"(null)"]){
        return  YES;
    }
    if([self isEqualToString:@"<null>"]){
        return  YES;
    }
    if (self.length == 0 || [[self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0){
        return  YES;
    }
    return NO;
}