Handle invalid vendordep JSON files better

[rzblue]

Missing/incorrect keys usually results in a difficult to debug NPE when the value is accessed.

[sciencewhiz]

It looks like there's code to throw exceptions for many errors. Do you have examples of files that have NPEs?

native-utils/src/main/java/edu/wpi/first/nativeutils/vendordeps/WPIVendorDepsExtension.java

Lines 199 to 224 in d7a64d6

	if (dep.name == null) {
	throw new VendorParsingException(VendorParsingError.MissingName);
	}
	String filename = dep.name;
	if (dep.mavenUrls == null) {
	throw new VendorParsingException(filename, VendorParsingError.NoMavenUrl);
	}
	// Enumerate all group ids
	Set<String> groupIds = new HashSet<>();
	if (dep.cppDependencies == null) {
	throw new VendorParsingException(filename, VendorParsingError.MissingCppDeps);
	}
	for (CppArtifact cpp : dep.cppDependencies) {
	groupIds.add(cpp.groupId);
	}
	if (dep.jniDependencies == null) {
	throw new VendorParsingException(filename, VendorParsingError.MissingJniDeps);
	}
	for (JniArtifact jni : dep.jniDependencies) {
	groupIds.add(jni.groupId);
	}
	if (dep.javaDependencies == null) {
	throw new VendorParsingException(filename, VendorParsingError.MissingJavaDeps);
	}