“Otherwise” argument of my IF-function applies to blank cells, but should ignore them. What can I add to my formula to stop it?

In my IF-function the “otherwise” argument should conduct the subtraction “6 - value”. It works fine for cells containing numbers, but unfortunately also works fine with blank cells. This results in a lot of cells with 6 (6 - 0 = 6) instead of empty cells.

In detail: I want to import and select data collected in an online questionnaire. I import my extract of the raw data in sheet “Sample” with the following formula:

=IF(LOOKUP(D$1,'Analysis'!$A$2:$A,'Analysis'!$G$2:$G)="No",FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0),ARRAYFORMULA(6-FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0)))

= If the question has not to be reversed (“No”), then import the values as they are, otherwise (if the question has to be reversed, “Yes”) subtract 6 - value.

Sheets in Google Spreadsheets:

• “Import”: This sheet contains the raw data. For each person that participated in the study, there is a row with the corresponding answers (that is 1, 2, 3, 4 or 5 according to the rating scale in the questionnaire). Because not every person in the list started or completed the questionnaire, there are blank cells where no answers were registered.
• “Sample”: This sheet should contain an extract of the raw data for further analysis. It’s the sheet where the IF-formula is applied.
• “Analysis”: This sheet contains informations concerning the questions, e.g. if the answers of some questions have to be reversed (reversed rating scale: 1 -> 5, 2 -> 4, 3 stays 3 and so on).

Coordinates:

• Sheet “Sample”: Cell D$1, E$1, F$1 and so on contain the names of the questions (e.g. question_1).
• Sheet “Analysis”: A2 to A contain the names of the questions.
• Sheet “Analysis”: G2 to G contain the information if the answers of the questions have to be reversed. If the answers have to be reversed (“Yes”), the raw data needs to be adjusted with “6-” (6-5 = 1, 6-4 = 2, 6-3 = 3 and so on).
• Sheet “Import”: A2 to A contains if there are any missing values. Zero means there are no missing values. Only data rows with no missing values should be imported.

Problem: The formula works fine and displays the answers and reversed answers for the questions of interest. BUT at the end of the sheet “Sample” the columns continue with 6, 6, 6, 6, 6, 6, 6… (only for reversed questions); for not reversed questions the cells after the last valid import are blank.

Attempts to fix it: I tried different variations of nested if-functions that unfortunately don’t have any effect, e.g.:

=IF(ISBLANK(Import!E2:I8)," ",IF(LOOKUP(D$1,Analysis!$A$2:$A,Analysis!$G$2:$G)="No",FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0),ARRAYFORMULA(6-FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0))))

or:

=IF(LOOKUP(D$1,Analysis!$A$2:$A,Analysis!$G$2:$G)="No",FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0),IF(Import!E2:E=" "," ",ARRAYFORMULA(6-FILTER(FILTER(Import!$A$2:$CV,Import!$A$1:$CV$1=D$1),Import!$A$2:$A=0))))

Alternatively, I could delete the cells with 6, 6, 6,… but that would be very time-consuming for all questionnaires.

Thanks for your help!