code: void checkFrameValue(final Object value) {
          if (value == Opcodes.TOP || value == Opcodes.INTEGER
                  || value == Opcodes.FLOAT || value == Opcodes.LONG
                  || value == Opcodes.DOUBLE || value == Opcodes.NULL
                  || value == Opcodes.UNINITIALIZED_THIS) {
              return;
          }
          if (value instanceof String) {
              checkInternalName((String) value, "Invalid stack frame value");
              return;
          }
          if (!(value instanceof Label)) {
              throw new IllegalArgumentException("Invalid stack frame value: "
                      + value);
          } else {
              usedLabels.add((Label) value);
          }
      }
docs: Checks a stack frame value.
  
  @param value
  the value to be checked.