Nulls

[Brian Goetz]

Trying again to categorize the choices and identify pros/cons...

Seems like there are four buckets here:

1.  Ban nulls.  This means that feeding nulls into a Stream MUST produce 
an NPE.

2.  Ignore nulls.

3.  Tolerate nulls.  Streams API takes no position on nulls, but may 
well pass elements to less tolerant destinations (e.g., user-provided 
lambdas, user-provided collections, Optional constructor.)  Nulls may 
cause NPEs in these cases.

4.  Embrace nulls.  Ensure that every operation can deal with nulls in a 
well-defined manner.  (This entails, for example, either dropping the 
Optional-bearing methods or making present Optional deal with null.)


I think its safe to say that for each of these, there is some subset of 
us who finds it undesirable.

Doug proposed (2) and (4).  I proposed (3).  Nearly everyone has some 
sympathy for (1) but no one really wants to be that intolerant.


Attempted summary of pros/cons:

1 PRO: Predictable, simple
1 CON: Might be overly harsh, interferes with when user might actually 
want to see nulls and can deal accordingly

2 PRO: Simple
2 CON: size() lies, interferes with optimizations, interferes with when 
user might actually want to see nulls and can deal accordingly

3 PRO: Minimizes distortion on API, implementation in the null-free case
3 CON: more complex reasoning about what might happen, op behavior may 
change subtly over time as implementation changes

4 PRO: Predictable
4 CON: sacrifices functionality/safety for sake of a corner case