diff --git a/src/checkers/inference/DefaultSlotManager.java b/src/checkers/inference/DefaultSlotManager.java
index 0b7993010..c9017d271 100644
--- a/src/checkers/inference/DefaultSlotManager.java
+++ b/src/checkers/inference/DefaultSlotManager.java
@@ -245,6 +245,9 @@ public Slot getVariableSlot( final AnnotatedTypeMirror atm ) {
      */
     @Override
     public Slot getSlot( final AnnotationMirror annotationMirror ) {
+    	if (annotationMirror == null) {
+    		return null;
+    	}
 
         final int id;
         if (InferenceQualifierHierarchy.isVarAnnot(annotationMirror)) {
@@ -349,7 +352,12 @@ public RefinementVariableSlot createRefinementVariableSlot(AnnotationLocation lo
             addToSlots(refinementVariableSlot);
         } else if (locationCache.containsKey(location)) {
             int id = locationCache.get(location);
-            refinementVariableSlot = (RefinementVariableSlot) getSlot(id);
+            if (getSlot(id) instanceof RefinementVariableSlot) {
+            	refinementVariableSlot = (RefinementVariableSlot) getSlot(id);
+            } else {
+            	refinementVariableSlot = new RefinementVariableSlot(location, nextId(), refined);
+                addToSlots(refinementVariableSlot);
+            }
         } else {
             refinementVariableSlot = new RefinementVariableSlot(location, nextId(), refined);
             addToSlots(refinementVariableSlot);
diff --git a/src/checkers/inference/InferenceQualifierHierarchy.java b/src/checkers/inference/InferenceQualifierHierarchy.java
index 5d0f535bd..1a46fb90d 100644
--- a/src/checkers/inference/InferenceQualifierHierarchy.java
+++ b/src/checkers/inference/InferenceQualifierHierarchy.java
@@ -221,6 +221,11 @@ public boolean isSubtype(final AnnotationMirror subtype, final AnnotationMirror
 
         final Slot subSlot   = slotMgr.getSlot(subtype);
         final Slot superSlot = slotMgr.getSlot(supertype);
+        
+        // TODO: remove hack
+        if (subSlot == null || superSlot == null) {
+        	return true;
+        }
 
         return constraintMgr.addSubtypeConstraintNoErrorMsg(subSlot, superSlot);
     }
diff --git a/src/checkers/inference/InferenceVisitor.java b/src/checkers/inference/InferenceVisitor.java
index 2914c6f01..0ddeed9ba 100644
--- a/src/checkers/inference/InferenceVisitor.java
+++ b/src/checkers/inference/InferenceVisitor.java
@@ -658,9 +658,10 @@ public boolean maybeAddRefinementVariableConstraints(final AnnotatedTypeMirror v
 
                     Slot sub = slotManager.getVariableSlot(upperBound);
                     logger.fine("InferenceVisitor::commonAssignmentCheck: Equality constraint for qualifiers sub: " + sub + " sup: " + sup);
-
-                    // Equality between the refvar and the value
-                    constraintManager.addEqualityConstraint(sup, sub);
+                    if (sub != null) {
+                    	// Equality between the refvar and the value
+                        constraintManager.addEqualityConstraint(sup, sub);
+                    }
 
                     // Refinement variable still needs to be a subtype of its declared type value
                     constraintManager.addSubtypeConstraint(sup, ((RefinementVariableSlot) sup).getRefined());
diff --git a/src/checkers/inference/VariableAnnotator.java b/src/checkers/inference/VariableAnnotator.java
index 1dc7e511b..14b953c1f 100644
--- a/src/checkers/inference/VariableAnnotator.java
+++ b/src/checkers/inference/VariableAnnotator.java
@@ -1017,6 +1017,9 @@ public boolean enclosedByAnnotation(TreePath path) {
         treeKinds.add(Kind.METHOD);
         treeKinds.add(Kind.CLASS);
         Tree enclosure = TreeUtils.enclosingOfKind(path, treeKinds);
+        if (enclosure == null) {
+        	return false;
+        }
         return enclosure.getKind() == Kind.ANNOTATION
             || enclosure.getKind() == Kind.ANNOTATION_TYPE
             || enclosure.getKind() == Kind.TYPE_ANNOTATION;