diff --git a/java/com/google/turbine/model/TurbineConstantTypeKind.java b/java/com/google/turbine/model/TurbineConstantTypeKind.java
index bb5bea15..8968a4db 100644
--- a/java/com/google/turbine/model/TurbineConstantTypeKind.java
+++ b/java/com/google/turbine/model/TurbineConstantTypeKind.java
@@ -27,7 +27,7 @@ public enum TurbineConstantTypeKind {
   BOOLEAN("boolean"),
   BYTE("byte"),
   STRING("String"),
-  NULL("null");
+  NULL("<nulltype>");
 
   private final String name;
 
diff --git a/java/com/google/turbine/processing/TurbineTypeMirror.java b/java/com/google/turbine/processing/TurbineTypeMirror.java
index 8352850f..a0ee3ffa 100644
--- a/java/com/google/turbine/processing/TurbineTypeMirror.java
+++ b/java/com/google/turbine/processing/TurbineTypeMirror.java
@@ -527,7 +527,7 @@ public TypeMirror getUpperBound() {
     public TypeMirror getLowerBound() {
       return info().lowerBound() != null
           ? factory.asTypeMirror(info().lowerBound())
-          : factory.noType();
+          : factory.nullType();
     }
 
     @Override
diff --git a/java/com/google/turbine/processing/TurbineTypes.java b/java/com/google/turbine/processing/TurbineTypes.java
index 13458ec8..0e639584 100644
--- a/java/com/google/turbine/processing/TurbineTypes.java
+++ b/java/com/google/turbine/processing/TurbineTypes.java
@@ -413,7 +413,8 @@ private boolean isArraySubtype(ArrayTy a, Type b, boolean strict) {
   // https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.10.1
   private static boolean isPrimSubtype(PrimTy a, Type other) {
     if (other.tyKind() != TyKind.PRIM_TY) {
-      return false;
+      // The null reference can always be assigned or cast to any reference type, see JLS 4.1
+      return a.primkind() == TurbineConstantTypeKind.NULL && isReferenceType(other);
     }
     PrimTy b = (PrimTy) other;
     switch (a.primkind()) {
@@ -483,7 +484,7 @@ private static boolean isPrimSubtype(PrimTy a, Type other) {
       case BOOLEAN:
         return a.primkind() == b.primkind();
       case NULL:
-        break;
+        return isReferenceType(other);
     }
     throw new AssertionError(a.primkind());
   }
@@ -672,8 +673,12 @@ public boolean isAssignable(TypeMirror a1, TypeMirror a2) {
   private boolean isAssignable(Type t1, Type t2) {
     switch (t1.tyKind()) {
       case PRIM_TY:
+        TurbineConstantTypeKind primkind = ((PrimTy) t1).primkind();
+        if (primkind == TurbineConstantTypeKind.NULL) {
+          return isReferenceType(t2);
+        }
         if (t2.tyKind() == TyKind.CLASS_TY) {
-          ClassSymbol boxed = boxedClass(((PrimTy) t1).primkind());
+          ClassSymbol boxed = boxedClass(primkind);
           t1 = ClassTy.asNonParametricClassTy(boxed);
         }
         break;
@@ -700,6 +705,14 @@ private static boolean isObjectType(Type type) {
     return type.tyKind() == TyKind.CLASS_TY && ((ClassTy) type).sym().equals(ClassSymbol.OBJECT);
   }
 
+  private static boolean isReferenceType(Type type) {
+    return switch (type.tyKind()) {
+      case CLASS_TY, ARRAY_TY, TY_VAR, WILD_TY, INTERSECTION_TY, ERROR_TY -> true;
+      case PRIM_TY -> ((PrimTy) type).primkind() == TurbineConstantTypeKind.NULL;
+      case NONE_TY, METHOD_TY, VOID_TY -> false;
+    };
+  }
+
   @Override
   public boolean contains(TypeMirror a, TypeMirror b) {
     return contains(asTurbineType(a), asTurbineType(b), /* strict= */ true);
diff --git a/java/com/google/turbine/type/Type.java b/java/com/google/turbine/type/Type.java
index 41d8b7b4..51b76c17 100644
--- a/java/com/google/turbine/type/Type.java
+++ b/java/com/google/turbine/type/Type.java
@@ -308,6 +308,8 @@ public final String toString() {
   }
 
   /** A primitive type. */
+  // TODO: cushon - consider renaming this, since it models things like String and null that can
+  // appear as constants and not primitives.
   @AutoValue
   abstract class PrimTy implements Type {
 
diff --git a/javatests/com/google/turbine/processing/AbstractTurbineTypesTest.java b/javatests/com/google/turbine/processing/AbstractTurbineTypesTest.java
index 307b71ad..822283b3 100644
--- a/javatests/com/google/turbine/processing/AbstractTurbineTypesTest.java
+++ b/javatests/com/google/turbine/processing/AbstractTurbineTypesTest.java
@@ -462,6 +462,9 @@ public CharSequence getCharContent(boolean ignoreEncodingErrors) {
 
   /**
    * Discover all types contained in the given element, keyed by their immediate enclosing element.
+   *
+   * <p>This method is executed for both javac and Turbine and is expected to produce the same
+   * results in each case.
    */
   private static void getTypes(
       Types typeUtils, Element element, Multimap<String, TypeMirror> types) {
@@ -508,6 +511,7 @@ public Void visitTypeVariable(TypeVariable t, Void aVoid) {
                       if (t.getUpperBound() != null) {
                         types.put(key(e), t.getUpperBound());
                       }
+                      types.put(String.format("getLowerBound(%s)", key(e)), t.getLowerBound());
                       return null;
                     }
                   },
diff --git a/javatests/com/google/turbine/processing/TurbineTypeMirrorTest.java b/javatests/com/google/turbine/processing/TurbineTypeMirrorTest.java
index bf08f899..787e9cf9 100644
--- a/javatests/com/google/turbine/processing/TurbineTypeMirrorTest.java
+++ b/javatests/com/google/turbine/processing/TurbineTypeMirrorTest.java
@@ -226,7 +226,7 @@ public void tyVar() {
                         .getTypeParameters())
                 .asType();
     assertThat(t.getKind()).isEqualTo(TypeKind.TYPEVAR);
-    assertThat(t.getLowerBound().getKind()).isEqualTo(TypeKind.NONE);
+    assertThat(t.getLowerBound().getKind()).isEqualTo(TypeKind.NULL);
     assertThat(t.getUpperBound().toString()).isEqualTo("java.lang.Comparable<? super T>");
   }
 
diff --git a/pom.xml b/pom.xml
index d78c0f34..12fa494c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -296,7 +296,7 @@
         <artifactId>maven-javadoc-plugin</artifactId>
         <version>3.3.1</version>
         <configuration>
-          <source>8</source>
+          <source>16</source>
           <detectJavaApiLink>false</detectJavaApiLink>
           <notimestamp>true</notimestamp>
           <doctitle>turbine ${project.version} API</doctitle>