Improving null-safety of isEqualToNormalizingNewlines

[Nacho321]

Improving the null-safety in isEqualToNormalizingNewlines to avoid NPE errors when actual and/or expected are null.

Check List:

• Fixes Improve null-safety of isEqualToNormalizingNewlines #2775
• Unit tests : YES
• Javadoc with a code example (on API only) : NA
• PR meets the contributing guidelines

[marcela-cardona-s]

Hello, I was reviewing the proposed solution and found that the cyclomatic complexity was increased from 3 to 14, so I propose a more optimal solution, keeping the complexity at 3. You can use the "CodeMetrics" plugin in IntelliJ Idea to validate this value. I leave you the commit of my repository where I propose the solution.

[joel-costigliola]

Thanks @Nacho321 and @marcela-cardona-s, I have integrated this PR wiht both of you as authors.