[animated_collection] 🐛 Fix AnimatedValueWidget with first value being null

[ValentinVignal]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 75.96%. Comparing base (7d09d04) to head (fe6da1f).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
...ted_collection/lib/src/widgets/animated_value.dart	87.09%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #69      +/-   ##
==========================================
+ Coverage   74.65%   75.96%   +1.31%     
==========================================
  Files          18       17       -1     
  Lines         505      516      +11     
==========================================
+ Hits          377      392      +15     
+ Misses        128      124       -4     

Flag	Coverage Δ
animated_collection	75.96% <90.00%> (+1.31%)	⬆️
imperative_page_routes	75.96% <90.00%> (+1.31%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...d_collection/lib/src/widgets/animated_boolean.dart	100.00% <100.00%> (ø)
...ted_collection/lib/src/widgets/animated_color.dart	100.00% <100.00%> (ø)
...ted_collection/lib/src/widgets/animated_value.dart	91.48% <87.09%> (+0.18%)	⬆️

... and 2 files with indirect coverage changes

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