NLP in UpgradeUnmanagedSpringProject recipe, if managed dependency is not found

[ashakirin]

Applying UpgradeUnmanagedSpringProject for open source project is https://github.com/corona-warn-app/cwa-server throws the following exception:

Caused by: org.openrewrite.UncaughtVisitorException: java.lang.NullPointerException: Cannot invoke "org.openrewrite.maven.tree.ResolvedManagedDependency.getGroupId()" because "managedDependency" is null
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:253)
	at org.openrewrite.TreeVisitor.visitAndCast(TreeVisitor.java:285)
	at org.openrewrite.xml.XmlVisitor.lambda$visitTag$2(XmlVisitor.java:91)
	at org.openrewrite.internal.ListUtils.lambda$map$0(ListUtils.java:141)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:123)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:141)
	at org.openrewrite.xml.XmlVisitor.visitTag(XmlVisitor.java:91)
	at org.openrewrite.maven.MavenIsoVisitor.visitTag(MavenIsoVisitor.java:38)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:149)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:146)
	at org.openrewrite.xml.tree.Xml$Tag.acceptXml(Xml.java:448)
	at org.openrewrite.xml.tree.Xml.accept(Xml.java:55)
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:206)
	at org.openrewrite.TreeVisitor.visitAndCast(TreeVisitor.java:285)
	at org.openrewrite.xml.XmlVisitor.lambda$visitTag$2(XmlVisitor.java:91)
	at org.openrewrite.internal.ListUtils.lambda$map$0(ListUtils.java:141)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:123)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:141)
	at org.openrewrite.xml.XmlVisitor.visitTag(XmlVisitor.java:91)
	at org.openrewrite.maven.MavenIsoVisitor.visitTag(MavenIsoVisitor.java:38)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:149)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:146)
	at org.openrewrite.xml.tree.Xml$Tag.acceptXml(Xml.java:448)
	at org.openrewrite.xml.tree.Xml.accept(Xml.java:55)
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:206)
	at org.openrewrite.TreeVisitor.visitAndCast(TreeVisitor.java:285)
	at org.openrewrite.xml.XmlVisitor.lambda$visitTag$2(XmlVisitor.java:91)
	at org.openrewrite.internal.ListUtils.lambda$map$0(ListUtils.java:141)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:123)
	at org.openrewrite.internal.ListUtils.map(ListUtils.java:141)
	at org.openrewrite.xml.XmlVisitor.visitTag(XmlVisitor.java:91)
	at org.openrewrite.maven.MavenIsoVisitor.visitTag(MavenIsoVisitor.java:38)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:149)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:146)
	at org.openrewrite.xml.tree.Xml$Tag.acceptXml(Xml.java:448)
	at org.openrewrite.xml.tree.Xml.accept(Xml.java:55)
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:206)
	at org.openrewrite.TreeVisitor.visitAndCast(TreeVisitor.java:285)
	at org.openrewrite.xml.XmlVisitor.visitDocument(XmlVisitor.java:71)
	at org.openrewrite.maven.MavenIsoVisitor.visitDocument(MavenIsoVisitor.java:23)
	at org.openrewrite.maven.MavenIsoVisitor.visitDocument(MavenIsoVisitor.java:20)
	at org.openrewrite.xml.tree.Xml$Document.acceptXml(Xml.java:173)
	at org.openrewrite.xml.tree.Xml.accept(Xml.java:55)
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:206)
	at org.openrewrite.RecipeScheduler.lambda$scheduleVisit$5(RecipeScheduler.java:241)
	... 8 more
Caused by: java.lang.NullPointerException: Cannot invoke "org.openrewrite.maven.tree.ResolvedManagedDependency.getGroupId()" because "managedDependency" is null
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:153)
	at org.openrewrite.maven.spring.UpgradeUnmanagedSpringProject$2.visitTag(UpgradeUnmanagedSpringProject.java:146)
	at org.openrewrite.xml.tree.Xml$Tag.acceptXml(Xml.java:448)
	at org.openrewrite.xml.tree.Xml.accept(Xml.java:55)
	at org.openrewrite.TreeVisitor.visit(TreeVisitor.java:206)
	... 52 more```