Replace NULL macros with nullptr literals.

Change-Id: I918c40879aa547438f77e7d1a95fa2aa33bec398
diff --git a/api/gen_runtime.cpp b/api/gen_runtime.cpp
index 6a46f35..65682e5 100644
--- a/api/gen_runtime.cpp
+++ b/api/gen_runtime.cpp
@@ -693,7 +693,7 @@
     mLargestVersionNumber = 0;
     while (1) {
         Specification* spec = Specification::scanSpecification(specFile);
-        if (spec == NULL) {
+        if (spec == nullptr) {
             break;
         }
         getFunction(spec->getCleanName())->addSpecification(spec);
@@ -974,7 +974,7 @@
                 return spec;
             } else {
                 delete spec;
-                return NULL;
+                return nullptr;
             }
         }
 
@@ -1037,7 +1037,7 @@
     }
 
     delete spec;
-    return NULL;
+    return nullptr;
 }
 
 void Specification::writeFiles(ofstream& headerFile, ofstream& rsFile, ofstream& javaFile,