Method invocation may produce NullPointerException Retrofit Body

It is just a warning as it will never be null if the response is successful. You can ignore it or wrap around if(response.body() != null) to remove the warning.

Ads ads = response.body();
if(ads != null){
    constant.banner_on = ads.getBanner_on();
    // and so on.
}

Using if is great but there is only one line, much cleaner way is:

constant.banner_on = ads != null ? ads.getBanner_on() : null;

If you are using Java 8, you can do a assertion before assignment:

Ads ads = response.body();
assert ads != null;
constant.banner_on = ads.getBanner_on();

Another way to do this is using Objects.requireNonNull() before assignment:

constant.banner_on = Objects.requireNonNull(ads.getBanner_on());

That is actually designed primarily for param validation. Source code comment:

/**
     * Checks that the specified object reference is not {@code null}. This
     * method is designed primarily for doing parameter validation in methods
     * and constructors, as demonstrated below:
     * <blockquote><pre>
     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonNull(bar);
     * }
     * </pre></blockquote>
     * 

One great SO answer about this is here. Also read this to get understanding why we need to explicitly check..

Just use this null pointer check.

If(response != null && response.isSuccessfull())
{

// body

}