chore: fix tests, just call init() without arg instead of init(null)

Author: eduarddrenth

graphql-java-servlet/src/test/groovy/graphql/kickstart/servlet/AbstractGraphQLHttpServletSpec.groovy

@@ -1120,7 +1120,7 @@ b
       throw new TestException()
     }.build()).build()
     servlet = GraphQLHttpServlet.with(configuration)
-    servlet.init(null)
+    servlet.init()
 
     request.setPathInfo('/schema.json')
 

graphql-java-servlet/src/test/groovy/graphql/kickstart/servlet/TestUtils.groovy

@@ -62,7 +62,7 @@ class TestUtils {
         .with(contextBuilder)
         .with(executor())
         .build())
-    servlet.init(null)
+    servlet.init()
     return servlet
   }
 
@@ -86,7 +86,7 @@ class TestUtils {
             listeners
         )
     )
-    servlet.init(null)
+    servlet.init()
     return servlet
   }