Add extra check for std::nullopt in parse scale factor test

Author: adriazalvarez

qt/scientific_interfaces/ISISReflectometry/test/Reduction/ValidateRowTest.h

@@ -172,6 +172,7 @@ class ValidateRowTest : public CxxTest::TestSuite {
   void testParseScaleFactor() {
     TS_ASSERT(!parseScaleFactor("ABSC").second);
     TS_ASSERT(parseScaleFactor("").second);
+    TS_ASSERT_EQUALS(std::nullopt, parseScaleFactor("").first);
     TS_ASSERT_EQUALS(0.1, parseScaleFactor("0.1").first.value());
   }