Forgetful solution
by Kegler

Ten answers contain synonyms for “space” (shown in {}), and require the solver to “draw a blank” in lieu of
that synonym when entering the answer in the grid, as indicated by the center entry: COMING UP EMPTY.
The first letters of the ten affected clues (shown as X:) describe what the solver is entering: WHITE SPACE.

Forgetful solution grid

Across
1MAS + SAGE + D
8TUBA (ABUT rev)
12AP + PEND (PA rev)
14DEsIGNED
15SP(R)Y
17TEA ("TEE" hom)
18W: ME{GAP}HO(N)E (HOME PAGE anag)
19B(L)AH
20LLANO (hidden)
21REAP (PEAR anag)
24H: D{RIFT}WOOD (ODD WIT FOR anag)
25COMING UP EMPTY
29W + HOOPS
31N + APE
32I: C{(HO)LE}RIC
34kETCH
35LOOS + EST (SET anag)
38NO + R
40FAIR (2 defs)
41MO(SELL)E
42T: {B(LANK}E + T)ING (ANKLE anag)
43E: A{V(O)ID} + ED
44ESTRANGE (SERGEANT anag)
Down
1MAS + T (SAM rev)
2APPA + LOO + SA (PAPA anag; AS rev)
3SP + READ
4AN + GEL
5EDAM (DAME anag)
6DEF + END (FED rev)
7S: S(IN{GA + P})ORE
9UN + DOES
10B(E)AN
11ADZE ("ADS" hom)
13DIALOG (GOAL I'D anag)
16S(H,R)IMPER
17P: TH{RIFT}INESS (FINE T-SHIRTS anag)
19BACON (2 defs)
22ATT + ACHING
23PSYCH (1st letters)
26NACLE + L,E (CLEAN anag)
27A: P(OINT{B)LANK} (TOBIN anag)
28S(P)OUSE
29C: W{H(OLE}S)ALE (s/OLE/S)
30ST(R)AIN
33C + OWER
35L + AMA
36E: OBO{VOID} (BOO OVID anag)
37TIES (SITE anag)
39URG + E (RUG anag)