anchor.diff:  `foo()` returns `null`.
   
   |===
  +
  +NOTE: The algebraic operators can be used with any numeric type having a literal notation
  +(see <<data-literals,the data literals table>> ), including `java.math.BigInteger` and `java.math.BigDecimal`.
   
   The operator precedence rules are as follows:
   
  
positive.code: 
  |`+`|
  Addition on numbers and strings.|
  `1 + 2` gives 3.
  
  `"foo" + "bar"` gives `"foobar"`.
  
  
negative.code: |`java.lang.Double` | `1.234`, `-1.234`, `1.234e9`, ...
  
  |`java.lang.Float` | `1.234_F`, `-1.234_F`, `1.234e9_F`, ...
  
  |`java.math.BigInteger` | `1_B`, `-42_B`, `1_234_B`, ...
  
  |`java.math.BigDecimal` | `1.0_B`, `-1_234.56_B`, `1.234e-4_B`, ...
  
  |`java.lang.Class` | `String.class`, `java.lang.String.class`, `gololang.Predef.module`, ...
  
  