Fix NPE in CallResolver when MethodSignature.descriptor is null (#168)

Author: biancaisc

base/src/main/java/proguard/analysis/CallResolver.java

@@ -532,7 +532,8 @@ private void initArgumentsAndReturnValue(Call call) {
 
     call.setArguments(arguments);
 
-    if (target.descriptor.getReturnType().charAt(0) != TypeConstants.VOID
+    if (target.descriptor != null
+        && target.descriptor.getReturnType().charAt(0) != TypeConstants.VOID
         && particularValueEvaluationSuccessful) {
       call.setReturnValue(
           PartialEvaluatorUtils.getStackValue(
@@ -542,7 +543,8 @@ private void initArgumentsAndReturnValue(Call call) {
 
   private List<Value> getArguments(
       CodeLocation location, MethodSignature invokedMethodSig, boolean isStaticCall) {
-    if (invokedMethodSig.descriptor.getArgumentTypes() == null) {
+    if (invokedMethodSig.descriptor == null
+        || invokedMethodSig.descriptor.getArgumentTypes() == null) {
       log.warn("Argument types list of {} is null!", invokedMethodSig);
       return Collections.emptyList();
     }