code: public static boolean containsOnly (@Nullable final CharSequence aCS, @Nullable final ICharPredicate aFilter)
    {
      final int nLen = getLength (aCS);
      if (nLen == 0)
        return false;
  
      if (aFilter == null)
        return true;
  
      for (int i = 0; i < nLen; ++i)
        if (!aFilter.test (aCS.charAt (i)))
          return false;
      return true;
    }
docs: Check if the passed {@link CharSequence} contains only characters matching
  the provided filter.
  
  @param aCS
  String to check. May be <code>null</code>.
  @param aFilter
  The filter to use. May be <code>null</code>.
  @return <code>true</code> if the filter is <code>null</code> and the string
  is not empty. <code>true</code> if the filter is not
  <code>null</code> and the string has at least one character and all
  characters of the string match the filter. <code>false</code>
  otherwise.
  @since 9.1.7