A DESCRIPTION OF THE PROBLEM :
For method com.sun.xml.internal.dtdparser.XmlNames.isName tools.jar of jdk1.8.0_301, test failed with empty input.
I think you it will be better if judge the input string is empty or not. Not to mention that it has already judged whether it is null.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
the test case:
 @Test
    public void test_isName_2_2(){

        String string0 = "";
        com.sun.xml.internal.dtdparser.XmlNames.isName(string0);
    }


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
return false
ACTUAL -
java.lang.StringIndexOutOfBoundsException: String index out of range: 0

at java.base/java.lang.StringLatin1.charAt(StringLatin1.java:48)
at java.base/java.lang.String.charAt(String.java:711)
at com.sun.xml.internal.dtdparser.XmlNames.isName(XmlNames.java:51)

---------- BEGIN SOURCE ----------
public static boolean isName(String value) {
        if (value == null) {
            return false;
        } else {
            char c = value.charAt(0);
            if (!XmlChars.isLetter(c) && c != '_' && c != ':') {
                return false;
            } else {
                for(int i = 1; i < value.length(); ++i) {
                    if (!XmlChars.isNameChar(value.charAt(i))) {
                        return false;
                    }
                }

                return true;
            }
        }
    }
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
public static boolean isName(String value) {
        if (value == null || value.isEmpty() ) {
            return false;
        } else {
            char c = value.charAt(0);
            if (!XmlChars.isLetter(c) && c != '_' && c != ':') {
                return false;
            } else {
                for(int i = 1; i < value.length(); ++i) {
                    if (!XmlChars.isNameChar(value.charAt(i))) {
                        return false;
                    }
                }

                return true;
            }
        }
    }