Tweak Guice to suggest toProvider(() -> null) rather than toProvider(Providers.of(null)).

core/src/com/google/inject/internal/AbstractBindingBuilder.java

@@ -41,7 +41,7 @@ public abstract class AbstractBindingBuilder<T> {
   public static final String SCOPE_ALREADY_SET = "Scope is set more than once.";
   public static final String BINDING_TO_NULL =
       "Binding to null instances is not allowed. "
-          + "Use toProvider(Providers.of(null)) if this is your intended behaviour.";
+          + "Use toProvider(() -> null) if this is your intended behaviour.";
   public static final String CONSTANT_VALUE_ALREADY_SET = "Constant value is set more than once.";
   public static final String ANNOTATION_ALREADY_SPECIFIED =
       "More than one annotation is specified for this binding.";

core/test/com/google/inject/BinderTest.java

@@ -223,8 +223,8 @@ public void configure() {
     } catch (CreationException expected) {
       assertContains(
           expected.getMessage(),
-          "1) Binding to null instances is not allowed. Use toProvider(Providers.of(null))",
-          "2) Binding to null instances is not allowed. Use toProvider(Providers.of(null))");
+          "1) Binding to null instances is not allowed. Use toProvider(() -> null)",
+          "2) Binding to null instances is not allowed. Use toProvider(() -> null)");
     }
   }