title: NSString "nil or empty" check -- is this complete?
body: <p>I was writing a small Category on NSString, and I wanted to know if this method is accurately handles all potential use cases:</p>
  
  <p><strong>Update:</strong> to clarify -- I wanted to make sure I'm not missing some oddball case involving character encodings, etc..</p>
  
  <pre><code>@implementation NSString (Helpers)
  
  +(BOOL)stringIsNilOrEmpty:(NSString*)aString {
      if (!aString)
          return YES;
      return [aString isEqualToString:@""];
  }
  @end
  </code></pre>
  
  <p>Sample usage:</p>
  
  <pre><code>-(void) sampleUsage {
      NSString *emptyString = @"";
      NSString *nilString = nil;
      NSAssert([NSString stringIsNilOrEmpty:nilString] == YES, @"String is nil/empty");
      NSAssert([NSString stringIsNilOrEmpty:emptyString] == YES, @"String is nil/empty");
  }
  @end
  </code></pre>