Avoid NPE on missing method type in JodaTimeVisitor

Author: timtebeek

src/main/java/org/openrewrite/java/migrate/joda/JodaTimeVisitor.java

@@ -168,7 +168,8 @@ public Javadoc visitReference(Javadoc.Reference reference, ExecutionContext ctx)
         J.MethodInvocation m = (J.MethodInvocation) super.visitMethodInvocation(method, ctx);
 
         // internal method with Joda class as return type
-        if (!method.getMethodType().getDeclaringType().isAssignableFrom(JODA_CLASS_PATTERN) &&
+        if (method.getMethodType() != null &&
+                !method.getMethodType().getDeclaringType().isAssignableFrom(JODA_CLASS_PATTERN) &&
                 method.getType().isAssignableFrom(JODA_CLASS_PATTERN)) {
             return migrateNonJodaMethod(method, m);
         }