Possible NPE in Expression.isNumber when passing an empty string
@@ -1048,7 +1048,7 @@ public class Expression {
* @return <code>true</code>, if the input string is a number.
*/
private boolean isNumber(String st) {
- if (st.charAt(0) == minusSign && st.length() == 1)
+ if (st == null || st.isEmpty() || st.charAt(0) == minusSign && st.length() == 1)
return false;
for (char ch : st.toCharArray()) {
if (!Character.isDigit(ch) && ch != minusSign
