Improper use of isUpperCase in the Java 'Validation' challenge. Please help!

public class TeacherAssistant { 

  public static String validatedFieldName(String fieldName) { 
    // These things should be verified: 
    // 1.  Member fields must start with an 'm' 
    // 2.  The second letter in the field name must be uppercased to ensure camel-casing 
    // NOTE:  To check if something is not equal use the != symbol. eg: 3 != 4 


if(fieldName.charAt(0)!='m'){
  throw new IllegalArgumentException("Doesnt start with m");
}

char secondLetter = fieldName.charAt(1); 
if(secondLetter.isUpperCase == false){
throw new IllegalArgumentException("Non-CamelCased");
}
    return fieldName;
  }

}