code: public TypeParserBuilder setNullStringStrategy(NullStringStrategy nullStringStrategy) {
          if (nullStringStrategy == null) {
              throw new NullPointerException(makeNullArgumentErrorMsg("nullStringStrategy"));
          }
          this.nullStringStrategy = nullStringStrategy;
          return this;
      }
docs: Set a custom made {@link NullStringStrategy} implementation to be used by the
  {@link TypeParser}.
  <p>
  The {@link NullStringStrategy} defines the string that will cause the {@link TypeParser} to
  return either an empty type (applicable for {@link Collection}, {@link Map} and Array types)
  or a null object. This String is known as the <code>NullString</code>.
  <p/>
  By default the <code>NullString</code> is set to the (trimmed and case insensitive) string
  "null". Examples follow: <br />
  <code>
  TypeParser parser = TypeParser.newBuilder().build();<br/>
  parser.parse("null", Integer.class); // returns a null object<br/>
  parser.parse("NULL", new {@code GenericType<List<Integer>>}() {}); // returns an empty List<br/>
  parser.parse(" null ", Integer[].class); // returns an empty Integer array<br/>
  </code>
  Use this method to set your own {@link InputPreprocessor} implementation to override the
  default behavior.
  
  @param nullStringStrategy {@link NullStringStrategy} implementation.
  @return {@link TypeParserBuilder}
  @throws NullPointerException if any given argument is null.
  @see NullStringStrategy