Misleading NullPointerException when reading an encrypted PEM key and none supplied

Describe the bug

When an encrypted PEM private key is used without supplying a password, a null pointer exception is being returned.

There is not way for the library user (an probably my end users too) to know the reason of this failure is that a password is required.

To Reproduce

            X509ExtendedKeyManager[] x509ExtendedKeyManager = {PemUtils.loadIdentityMaterial(
                        "certs.crt",
                        "encrypted.private.key",
                        null)};
                        
                     
            SSLContext context = SSLContext.getInstance("TLS");
            context.init(kmf.getKeyManagers(), null, null);

Results in :

java.lang.NullPointerException: null
        at java.base/java.util.Objects.requireNonNull(Objects.java:221)
        at nl.altindag.ssl.util.PemUtils.lambda$static$1(PemUtils.java:92)
        at nl.altindag.ssl.util.PemUtils.parsePrivateKey(PemUtils.java:416)
        at nl.altindag.ssl.util.PemUtils.parseIdentityMaterial(PemUtils.java:329)
        at nl.altindag.ssl.util.PemUtils.loadIdentityMaterial(PemUtils.java:301)
        at nl.altindag.ssl.util.PemUtils.loadIdentityMaterial(PemUtils.java:227)

Expected behavior

I expect a dedicated exception with an easy to understand message…

Environmental Data:

• Java 11 (OpenJDK 11.0.11)
• Maven 3.6.3
• Ubuntu

Additional context

I could end up using this library in a contribution to Apache James to not just support keystores but also PEM files.

The ease of use is appealing though I need users to understand by themselves their mistakes before reaching the community (including I) and says stuff like “your soft is not working there is a NPE” without understanding the mistake is theirs…

BTW I could fire a patch if my above proposal is deemed acceptable.

[chibenwa]

I did write https://github.com/Hakky54/sslcontext-kickstart/pull/114

[chibenwa]

NPE is IMO understandable to a developer doing debug while testing this newly written code, likely not to an admin blindly configuring this…

By the way nice to hear that you are planning to use this within an enterprise solution such as Apache James!

This yet have to pass review, today goal is to have a proof of concept :-p