Probably faster 4 comparisons instead of 6. Assuming that there is no overhead to calling ```.toString()``` on a string.

```
if (a is String) {
	return b != null ? a + b.toString() : a;
} 

if (a == null) {
	return b;
} 

if (b is String) {
	return b + a.toString();
} 

if (b == null) {
	return null;
}

return a + b;
```

I cannot run parser_pref for some reason, getting: 

```Unable to open file: C:/Users/Robert/Projects/Public/kasperl.angular.dart/gen/generated_functions.dart'file:///C:/Users/Robert/Projects/Public/kasperl.angular.dart/perf/parser_perf.dart': error: line 11 pos 1: library handler failed
import '../gen/generated_functions.dart' as generated_functions;```

Any advice?