code: public Class<?> getCommonPropertyType(ELContext context,
                                                 Object base) {
  
          if (base != null && base.getClass().isArray()) {
              return Integer.class;
          }
          return null;
      }
docs: If the base object is a Java language array, returns the most general
  type that this resolver accepts for the <code>property</code> argument.
  Otherwise, returns <code>null</code>.
  
  <p>Assuming the base is an array, this method will always return
  <code>Integer.class</code>. This is because arrays accept integers
  for their index.</p>
  
  @param context The context of this evaluation.
  @param base The array to analyze. Only bases that are a Java language
  array are handled by this resolver.
  @return <code>null</code> if base is not a Java language array;
  otherwise <code>Integer.class</code>.