Fix String Comparison

Author: rcosta358

liquidjava-verifier/src/main/java/liquidjava/processor/refinement_checker/RefinementTypeChecker.java

@@ -12,6 +12,8 @@
 import liquidjava.rj_language.BuiltinFunctionPredicate;
 import liquidjava.rj_language.Predicate;
 import liquidjava.rj_language.parsing.ParsingException;
+import liquidjava.utils.Utils;
+
 import org.apache.commons.lang3.NotImplementedException;
 import spoon.reflect.code.CtArrayRead;
 import spoon.reflect.code.CtArrayWrite;
@@ -264,10 +266,10 @@ public <T> void visitCtLiteral(CtLiteral<T> lit) {
             lit.putMetadata(REFINE_KEY, Predicate.createEquals(Predicate.createVar(WILD_VAR),
                     Predicate.createLit(lit.getValue().toString(), type)));
 
-        } else if (lit.getType().getQualifiedName().contentEquals("java.lang.String")) {
+        } else if (lit.getType().getQualifiedName().equals("java.lang.String")) {
             // Only taking care of strings inside refinements
-        } else if (type == "<nulltype>") {
-            // Skip null literals for now
+        } else if (type.equals(Utils.NULL_TYPE)) {
+            // Skip null literals
         } else {
             throw new NotImplementedException(
                     String.format("Literal of type %s not implemented:", lit.getType().getQualifiedName()));

liquidjava-verifier/src/main/java/liquidjava/utils/Utils.java

@@ -35,6 +35,7 @@ public class Utils {
     public static final String SHORT = "short";
     public static final String LONG = "long";
     public static final String FLOAT = "float";
+    public static final String NULL_TYPE = "<nulltype>";
 
     private static final Set<String> DEFAULT_NAMES = Set.of("old", "length", "addToIndex", "getFromIndex");