Modify rule S2225: Add VB.NET (#1062)

rules/S2225/vbnet/metadata.json

@@ -0,0 +1,3 @@
+{
+  "title": "\"ToString()\" method should not return Nothing"
+}

rules/S2225/vbnet/rule.adoc

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+Calling `ToString()` on an object should always return a string. Returning `Nothing` instead contravenes the method's implicit contract.
+
+== Noncompliant Code Example
+
+[source,vbnet]
+----
+Public Overrides Function ToString() As String
+    Return Nothing
+End Function
+----
+
+== Compliant Solution
+
+[source,vbnet]
+----
+Public Overrides Function ToString() As String
+    Return ""
+End Function
+----
+
+include::../see.adoc[]
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+include::../message.adoc[]
+
+'''
+== Comments And Links
+(visible only on this page)
+
+include::../comments-and-links.adoc[]
+endif::env-github,rspecator-view[]