Fix NPE in computing java version

Author: BoykoAlex

headless-services/jdt-ls-extension/org.springframework.tooling.jdt.ls.commons/src/org/springframework/tooling/jdt/ls/commons/classpath/ClasspathUtil.java

@@ -94,7 +94,8 @@ public static Classpath resolve(IJavaProject javaProject, Logger logger) throws
 				}
 			}
 		}
-		String javaVersion = extractJavaVersion(getJreContainer(javaProject.getRawClasspath()).getPath().lastSegment());
+		IClasspathEntry jreContainer = getJreContainer(javaProject.getRawClasspath());
+		String javaVersion = jreContainer == null ? null : extractJavaVersion(jreContainer.getPath().lastSegment());
 		Classpath classpath = new Classpath(cpEntries, javaVersion);
 		logger.debug("classpath=" + classpath.getEntries().size() + " entries");
 		return classpath;