Return null instead of false

[kylekatarnls]

Use stronger typing and null instead of false

[codecov-commenter]

Codecov Report

Merging #2340 (1f38f65) into 3.x (c93e4f6) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@              Coverage Diff              @@
##                3.x     #2340      +/-   ##
=============================================
+ Coverage     99.95%   100.00%   +0.04%     
=============================================
  Files           882       886       +4     
  Lines          8525      9269     +744     
=============================================
+ Hits           8521      9269     +748     
+ Misses            4         0       -4     

Impacted Files	Coverage Δ
src/Carbon/Carbon.php	100.00% <ø> (ø)
src/Carbon/CarbonImmutable.php	100.00% <ø> (ø)
src/Carbon/Cli/Invoker.php	100.00% <ø> (ø)
src/Carbon/Exceptions/NotACarbonClassException.php	100.00% <ø> (ø)
src/Carbon/Lang/aa_ET.php	100.00% <ø> (ø)
src/Carbon/Lang/am_ET.php	100.00% <ø> (ø)
src/Carbon/Lang/anp_IN.php	100.00% <ø> (ø)
src/Carbon/Lang/as_IN.php	100.00% <ø> (ø)
src/Carbon/Lang/ayc_PE.php	100.00% <ø> (ø)
src/Carbon/Lang/bhb_IN.php	100.00% <ø> (ø)
... and 310 more

---

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[spawnia]

I like where this is going, null is definitely more convenient then false, but why shouldn't methods such as create() always return a Carbon instance (or throw in case of invalid inputs)?

[kylekatarnls]

This is the planned progression: strict mode becomes true by default from 3.0.0 and disappears (to be always true) in 4.0.0, this means most of the method won't return null any longer (except make() or such which are very dedicated to that purpose).

Actually with the default strict mode already in 3.0.0 you can't get null from create()

[spawnia]

Got it, that makes a lot of sense to me. Good to see this library turning away from PHP's error swallowing legacy swamp.

[kylekatarnls]

This is hoping it will also evolve on PHP side because providing methods like createFromFormat(): Carbon|null while DateTime has createFromFormat(): DateTime|false is actually violating the Liskov Substitution Principle making Carbon a bit less compatible with its parent. 😞

So it will still need careful checking with dependent packages to validate we can keep it for the future stable release but I have good hope.