Library reports dev_status even when device is not present

[radio-miskovice]

I have a program that initializes CLK0, sets frequency and then it periodically reads device status, and sends some results to Serial.

It appears that even when I remove the Si5351 module, the program still reads some "status" (LOL_A = 0);

Expected behavior
I would expect some kind of error, to recognize the device is not present.

Code

#include <Wire.h>
#include "si5351.h"

/* Si5351 module */ 
#define VFO SI5351_CLK0 
uint64_t vfoFreq = 702130000ULL ;
bool vfoOk = false ;
Si5351 vfo ;

void setup() {
  uint8_t idev ;
  uint16_t dw ;
  // blinker & serial //
  pinMode( PC13, OUTPUT );
  digitalWrite( PC13, LOW );
  Serial.begin(115200);
  delay(10);
  Serial.println("started.");
  digitalWrite( PC13, HIGH );
  // I2C setup 
  // Wire.setSDA(PB9);
  // Wire.setSCL(PB8);
  Wire.begin();
  Serial.println("I2C bus on PB8, PB9");  
  Si5351A initalization 
  Serial.print("Si5351 ");
  if( checkI2C( 0x60 ) != 0 ) Serial.println("not ");
  Serial.println("present");  
  vfoOk = vfo.init(SI5351_CRYSTAL_LOAD_8PF, 0, 0) ;
  Serial.println( vfoOk ? "VFO OK" : "VFO ??" );
  vfo.set_freq( vfoFreq, VFO );  
  vfo.update_status();
  delay(1000);
}

uint8_t lastPllA = 0xFF ;
void loop() {
  Si5351Status st = vfo.dev_status ;
  vfo.update_status();
  if( st.LOL_A != lastPllA ) {
    Serial.printf( "VFO PLL A: %i\n", st.LOL_A ); 
    lastPllA = st.LOL_A ;
  }
  digitalWrite( PC13, LOW );
  vfo.output_enable( VFO, false );
  delay( 200 ); 
  readSerial();
}

void readSerial() {
  char text[40] = { 0 };
  byte inputSize = 0 ;
  if( Serial.available() ) {
    digitalWrite( PC13, HIGH );
    delay(100);
    inputSize = Serial.readBytesUntil( '\n', text, 39 );
    if( inputSize ) text[inputSize] = 0;
    Serial.print( "ECHO: "); Serial.println( text );
    delay(65);
    digitalWrite( PC13, LOW );
  }
}

uint8_t checkI2C( uint8_t addr ) {
  Wire.beginTransmission( addr );
  return Wire.endTransmission();
}