guava/src/com/google/common/base/Preconditions.java
@CanIgnoreReturnValue
  public static <T extends @NonNull Object> T checkNotNull(T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }
@CanIgnoreReturnValue
  public static <T extends @NonNull Object> T checkNotNull(T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }
Ensures that an object reference passed as a parameter to the calling method is not null.

@param reference an object reference
@return the non-null reference that was validated
@throws NullPointerException if {@code reference} is null
@see Verify#verifyNotNull Verify.verifyNotNull()