Ignore gcc-10 warning (#273)

Workaround for GCC 10 null dereference warning.

include/cxxopts.hpp

@@ -1133,6 +1133,11 @@ namespace cxxopts
       m_value->parse();
     }
 
+#if defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Werror=null-dereference"
+#endif
+    
     CXXOPTS_NODISCARD
     size_t
     count() const noexcept
@@ -1140,6 +1145,10 @@ namespace cxxopts
       return m_count;
     }
     
+#if defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
+
     // TODO: maybe default options should count towards the number of arguments
     CXXOPTS_NODISCARD
     bool