A DESCRIPTION OF THE PROBLEM :
The documentation for the BigInteger(String) constructor says:
> The String representation consists of an optional minus sign followed by a sequence of one or more decimal digits.
https://docs.oracle.com/en/java/javase/14/docs/api/java.base/java/math/BigInteger.html#%3Cinit%3E(java.lang.String)

However, it actually accepts not only a leading minus sign ('-') but also a leading plus sign ('+'). This is likely an oversight in the documentation because the BigInteger(String, int) constructor (to which the constructor delegates) explicitly mentions the leading plus sign.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Since "+5" is parsed successfully, the documentation should specify that a leading plus sign is allowed as well.

---------- BEGIN SOURCE ----------
new BigInteger("+5")
---------- END SOURCE ----------