src/main/java/org/fest/assertions/ThrowableAssert.java
public @NotNull ThrowableAssert hasNoCause() {
    isNotNull();
    Throwable actualCause = actual.getCause();
    if (actualCause == null) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("expected exception without cause, but cause was:<%s>", actualCause.getClass()));
  }
public @NotNull ThrowableAssert hasNoCause() {
    isNotNull();
    Throwable actualCause = actual.getCause();
    if (actualCause == null) {
      return this;
    }
    failIfCustomMessageIsSet();
    throw failure(format("expected exception without cause, but cause was:<%s>", actualCause.getClass()));
  }
Verifies that the actual {@code Throwable} does not have a cause.

@return this assertion object.
@throws AssertionError if the actual {@code Throwable} is {@code null}.
@throws AssertionError if the actual {@code Throwable} has a cause.