Review

UnionTypeBuilder.build() returns a JSType that can never be null. Branching on a null check therefore results in dead code.

Check Node.isNoType() instead.

• superfluous/condition/null_check

com/google/javascript/rhino/jstype/UnionType.java

meet(JSType)

class UnionType {
  JSType meet(JSType that) {
    UnionTypeBuilder builder = new UnionTypeBuilder(registry);
    for (JSType alternate : alternates) {
      if (alternate.isSubtype(that)) {
        builder.addAlternate(alternate);
      }
    }

    if (that instanceof UnionType) {
      for (JSType otherAlternate : ((UnionType) that).alternates) {
        if (otherAlternate.isSubtype(this)) {
          builder.addAlternate(otherAlternate);
        }
      }
    } else if (that.isSubtype(this)) {
      builder.addAlternate(that);
    }
    JSType result = builder.build();
    if (result != null) {
      return result;
    } else if (this.isObject() && that.isObject()) {
      return getNativeType(JSTypeNative.NO_OBJECT_TYPE);
    } else {
      return getNativeType(JSTypeNative.NO_TYPE);
    }
  }

}

public class IsNotType {	
	public JSType pattern(UnionTypeBuilder builder) {
    JSType result = builder.build();
    if(!result.isNoType()) {
      return result;
    } else {
      return null; // default value
    }
	}
}