Fixing project loading issues with micronaut complex project.

[sdedic]

The bug that provoked the investigation was

java.lang.NullPointerException
    at java.base/java.util.ArrayList.(ArrayList.java:179)
    at org.netbeans.modules.gradle.tooling.NbProjectInfoBuilder.detectSources(NbProjectInfoBuilder.java:1012)
    at org.netbeans.modules.gradle.tooling.NbProjectInfoBuilder.lambda$runAndRegisterPerf$9(NbProjectInfoBuilder.java:408)
    at org.netbeans.modules.gradle.tooling.NbProjectInfoBuilder.runAndRegisterPerf(NbProjectInfoBuilder.java:414)
    at org.netbeans.modules.gradle.tooling.NbProjectInfoBuilder.runAndRegisterPerf(NbProjectInfoBuilder.java:408)
    at org.netbeans.modules.gradle.tooling.NbProjectInfoBuilder.buildAll(NbProjectInfoBuilder.java:211)
    at org.netbeans.modules.gradle.tooling.NetBeansToolingPlugin$NetBeansToolingModelBuilder.buildAll(NetBeansToolingPlugin.java:71)

that was thrown when the project contained kotlin sources. The bug was introduced by a change in getProperty that stopped throwing exceptions on an unknown property, and started to return null instead. The PR just adapts the detectSource code to the new error reporting style.

During testing, I've noticed some other bad behaviour I have not seen before on certain projects:

• the task Map is not cloned on return by Gradle (it seems), so I've got a ConcurrentModificationException - apparently some of the looped-over calls lazy-populated the collection
• null default property value was not handled well (changed to Optional.ofNullable).

[lkishalmi]

Looks good to me.

[matthiasblaesing]

Looks sane to me