Marking the input version as @Nullable is incorrect.

[piotrooo]

If you pass in null to this method, it throws a NullPointerException as it fails to create a regex matcher:

java.lang.NullPointerException: Cannot invoke "java.lang.CharSequence.length()" because "this.text" is null
	at java.base/java.util.regex.Matcher.getTextLength(Matcher.java:1769)
	at java.base/java.util.regex.Matcher.reset(Matcher.java:415)
	at java.base/java.util.regex.Matcher.<init>(Matcher.java:252)
	at java.base/java.util.regex.Pattern.matcher(Pattern.java:1134)
	at org.semver4j.internal.Coerce.coerce(Coerce.java:20)
	at org.semver4j.Semver.coerce(Semver.java:89)

Originally posted by @NielsDoucet in #177 (comment)

[DIG-]

There is two ways to resolve:

• Mark param as NotNull
• Return null if null

[piotrooo]

I thought about returning null when parameter is null. There is no possibility for coercing version on nullable - it's impossible.

[NielsDoucet]

https://github.com/semver4j/semver4j/blob/main/src/test/java/org/semver4j/SemverTest.java#L743
I also noticed that there wasn't a test for these edge cases (like null and an empty string).

[piotrooo]

This's a major oversight...

[piotrooo]

Fixed in v5.2.2