Replace more NotProvided.INSTANCE block values with Nil.INSTANCE

These are the less obvious places where a `NotProvided` value is being
used to represent a block. I found them by doing a manual audit of
`NotProvided` uses.

Author: tomstuart

src/main/java/org/truffleruby/cext/CExtNodes.java

@@ -68,7 +68,6 @@
 import org.truffleruby.interop.TranslateInteropExceptionNode;
 import org.truffleruby.core.string.ImmutableRubyString;
 import org.truffleruby.language.LexicalScope;
-import org.truffleruby.language.NotProvided;
 import org.truffleruby.language.RubyContextNode;
 import org.truffleruby.language.RubyDynamicObject;
 import org.truffleruby.language.RubyGuards;
@@ -1119,7 +1118,7 @@ protected RubyClass classNew(RubyClass superclass) {
 
             RubyClass klass = (RubyClass) allocateNode
                     .call(getContext().getCoreLibrary().classClass, "__allocate__");
-            return initializeClassNode.executeInitialize(klass, superclass, NotProvided.INSTANCE);
+            return initializeClassNode.executeInitialize(klass, superclass, nil);
         }
 
     }

src/main/java/org/truffleruby/core/array/ArrayNodes.java

@@ -697,7 +697,7 @@ private Object delete(VirtualFrame frame, RubyArray array, Object value, Object
                 array.size = i;
                 return found;
             } else {
-                if (maybeBlock == NotProvided.INSTANCE) {
+                if (maybeBlock == nil) {
                     return nil;
                 } else {
                     return yield((RubyProc) maybeBlock, value);

src/main/java/org/truffleruby/core/hash/HashNodes.java

@@ -382,7 +382,7 @@ protected Object deletePackedArray(RubyHash hash, Object key, Object maybeBlock,
 
             assert HashOperations.verifyStore(getContext(), hash);
 
-            if (maybeBlock == NotProvided.INSTANCE) {
+            if (maybeBlock == nil) {
                 return nil;
             } else {
                 return yieldNode.executeDispatch((RubyProc) maybeBlock, key);
@@ -397,7 +397,7 @@ protected Object delete(RubyHash hash, Object key, Object maybeBlock) {
             final Entry entry = lookupResult.getEntry();
 
             if (entry == null) {
-                if (maybeBlock == NotProvided.INSTANCE) {
+                if (maybeBlock == nil) {
                     return nil;
                 } else {
                     return yieldNode.executeDispatch((RubyProc) maybeBlock, key);

src/main/java/org/truffleruby/core/inlined/InlinedCallNode.java

@@ -16,7 +16,6 @@
 import com.oracle.truffle.api.nodes.ExplodeLoop;
 
 import org.truffleruby.RubyLanguage;
-import org.truffleruby.language.NotProvided;
 import org.truffleruby.language.RubyNode;
 import org.truffleruby.language.dispatch.RubyCallNodeParameters;
 import org.truffleruby.language.methods.InternalMethod;
@@ -72,8 +71,7 @@ public Object execute(VirtualFrame frame) {
 
     public Object executeWithArgumentsEvaluated(VirtualFrame frame, Object receiverObject, Object blockObject,
             Object[] argumentsObjects) {
-        final Object blockArgument = blockObject == nil ? NotProvided.INSTANCE : blockObject;
-        return inlinedMethod.inlineExecute(frame, receiverObject, argumentsObjects, blockArgument);
+        return inlinedMethod.inlineExecute(frame, receiverObject, argumentsObjects, blockObject);
     }
 
     private Object executeBlock(VirtualFrame frame) {

src/main/java/org/truffleruby/core/method/MethodNodes.java

@@ -31,7 +31,6 @@
 import org.truffleruby.core.string.RubyString;
 import org.truffleruby.core.string.StringNodes;
 import org.truffleruby.core.symbol.RubySymbol;
-import org.truffleruby.language.NotProvided;
 import org.truffleruby.language.RubyContextSourceNode;
 import org.truffleruby.language.RubyRootNode;
 import org.truffleruby.language.Visibility;
@@ -134,7 +133,7 @@ public abstract static class CallNode extends CoreMethodArrayArgumentsNode {
         @Specialization
         protected Object call(VirtualFrame frame, RubyMethod method, Object[] arguments, Object maybeBlock) {
             return callBoundMethodNode
-                    .execute(frame, method, arguments, maybeBlock == NotProvided.INSTANCE ? nil : maybeBlock);
+                    .execute(frame, method, arguments, maybeBlock);
         }
 
     }

src/main/java/org/truffleruby/core/module/ModuleNodes.java

@@ -1224,7 +1224,7 @@ protected RubySymbol defineMethodBlock(
                 String name,
                 NotProvided proc,
                 RubyProc block) {
-            return defineMethodProc(frame, module, name, block, NotProvided.INSTANCE);
+            return defineMethodProc(frame, module, name, block, nil);
         }
 
         @Specialization