lib/plurimath/math/function/norm.rb in plurimath-0.2.0 vs lib/plurimath/math/function/norm.rb in plurimath-0.2.1

@@ -5,10 +5,11 @@
 module Plurimath
   module Math
     module Function
       class Norm < UnaryFunction
         def to_mathml_without_math_tag
-          "<mo>&#x2225;</mo>#{parameter_one.to_mathml_without_math_tag}<mo>&#x2225;</mo>"
+          first_value = parameter_one&.to_mathml_without_math_tag
+          "<mo>&#x2225;</mo>#{first_value}<mo>&#x2225;</mo>"
         end
       end
     end
   end
 end