Fix typo in NullTernary.md

This PR fixes a typo in the `NullTernary.md`.

Fixes google#4995

COPYBARA_INTEGRATE_REVIEW=google#4995 from izeye:patch-1 e035c29
PiperOrigin-RevId: 748735681

Author: izeye

docs/bugpattern/NullTernary.md

@@ -4,7 +4,7 @@ If a conditional expression evaluates to `null`, unboxing it will result in a
 For example:
 
 ```java
-int x = flag ? foo : null:
+int x = flag ? foo : null;
 ```
 
 If `flag` is false, `null` will be auto-unboxed from an `Integer` to `int`,