Fields, parameters and return values marked @NotNull, @NonNull, or @Nonnull are assumed to have non-null values and are not typically null-checked before use. Therefore setting one of these values to null, or failing to set such a class field in a constructor, could cause NullPointerExceptions at runtime.

Noncompliant Code Example

public class MainClass {

  @Nonnull
  private String primary;
  private String secondary;

  public MainClass(String color) {
    if (color != null) {
      secondary = null;
    }
    primary = color;  // Noncompliant; "primary" is Nonnull but could be set to null here
  }

  public MainClass() { // Noncompliant; "primary" Nonnull" but is not initialized
  }

  @Nonnull
  public String indirectMix() {
    String mix = null;
    return mix;  // Noncompliant; return value is Nonnull, but null is returned.}}
  }

See