What does "the hypotheses ... are verified as null" mean? Context:

This article examines the criterion-related validity of the results obtained by the application of four different methods of assessment to the correction of a second-year exam of
  translation into the foreign language (Spanish-English) done by 64 university students.
  These four methods are based on types currently used by university teachers, and the
  validation study is based on 17 external criteria taken from six different sources. In spite
  of this variety, a factor analysis reveals the presence of one main factor which is clearly
  identifiable as Translation Competence. The hypotheses regarding differences between the
  validity of the methods are verified as null, since all the systems, whether based on error
  analysis or a holistic approach, prove to correlate significantly with this main factor [Source]

What does the sentence in boldface mean?
 A: I've edited this, as what I said before was what I interpreted from the abstract. The rest of the analysis explains this better.
The three hypotheses that the bold line is referring to are verified by comparing the differences between the four methods. These hypotheses are not statistical hypotheses but exploratory hypotheses:

2.2. The three hypotheses
(1) The first hypothesis was that “It is possible to improve the quality of methods of correction based on
error analysis, if this analysis takes into account the possible
effect of the errors on the rest of the translation.” To verify this
hypothesis, the results obtained by Method A were compared to those
obtained by Method B.
(2) The second hypothesis was that “Methods of
assessment based on error analysis are more reliable and valid than
holistic methods.” To verify this hypothesis, the results obtained by
Methods A and B were compared to those obtained by Method C.
(3) The
third hypothesis was that “The quality of a translation can be
assessed more accurately if the method of assessment combines error
analysis with a holistic appreciation.” To verify this hypothesis, the
results obtained by Method A were compared to those obtained by Method
D.

These 4 methods check the validity of student translations of an authentic text done under exam conditions. "Validity" is the outcome (result) of each method.
This study did not detect differences between the results obtained by these 4 methods, and hence none of the 3 hypotheses were verified. This is what the bold line is stating.
