[TIMOB-6828] Setting value as nil removes header from request

[vishalduggal]

Fix for TIMOB-6828

[matt-langston]

Can you please use Objective-C literals and add debug logging. Something like this:

-(void)addHeaderKey:(NSString*)key andHeaderValue:(NSString*)value
{
    if (key == nil) {
        DebugLog(@"Ignore request to self.headers[%@] = %@", key, value);
        return;
    }

    if (value == nil) {
        DebugLog(@"Remove key %@ from self.headers (previous value of self.headers[%@] was %@", key, key, value);
        [self.headers removeObjectForKey:key];
    } else {
        DebugLog(@"self.headers[%@] = %@", key, value);
        self.headers[key] = value;
    }
}

[pec1985]

Code reviewed. Tested with Titanium Mobile. PR APPROVED!