The following works as expected when evaluated, but throws an error when compiling.

(defun hashmap-to-hashtable (hashmap &key (keyfun #'identity) (valfun #'identity) (invert? nil)
      &allow-other-keys &rest rest)
  (let ((keyset (#"keySet" hashmap))
(table (apply 'make-hash-table (remf :invert? (remf :valfun (remf :keyfun rest))))))
    (with-constant-signature ((iterator "iterator" t) (hasnext "hasNext") (next "next"))
      (loop with iterator = (iterator keyset)
while (hasNext iterator)
for item = (next iterator)
do (if invert?
(setf (gethash (funcall valfun (#"get" hashmap item)) table) (funcall keyfun item))
(setf (gethash (funcall keyfun item) table) (funcall valfun (#"get" hashmap item)))))
    table)))

-> Error

&REST/&BODY must be followed by a variable.
   [Condition of type PROGRAM-ERROR]

Restarts:
 0: [ABORT] Abort compilation.
 1: [ABORT] Return to SLIME's top level.
 2: [ABORT] Abort thread.

Backtrace:
  0: (SYSTEM:MAKE-CLOSURE (LAMBDA (#:G29656 &KEY (# NIL #:G29659) (# NIL #:G29661) (# NIL) &ALLOW-OTHER-KEYS ...) NIL) NIL)
  1: (JVM::P1-COMPILAND #S(JVM::COMPILAND :NAME HASHMAP-TO-HASHTABLE :LAMBDA-EXPRESSION (LAMBDA (#1=#:G29656 &KEY ((:KEYFUN #:G29658) NIL #:G29659) ((:VALFUN #:G29660) NIL #:G29661) ((:INVERT? #2=#:G29662)..
  2: (JVM::P1-FUNCTION #'(SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE (HASHMAP &KEY (KEYFUN #'IDENTITY) (VALFUN #'IDENTITY) (INVERT? NIL) &ALLOW-OTHER-KEYS ...) (BLOCK HASHMAP-TO-HASHTABLE (LET # #))))
  3: (JVM::P1 #'(SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE (HASHMAP &KEY (KEYFUN #'IDENTITY) (VALFUN #'IDENTITY) (INVERT? NIL) &ALLOW-OTHER-KEYS ...) (BLOCK HASHMAP-TO-HASHTABLE (LET # #))))
      Locals:
        "??" = "??"
  4: (JVM::P1 (SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE (HASHMAP &KEY (KEYFUN #'IDENTITY) (VALFUN #'IDENTITY) (INVERT? NIL) &ALLOW-OTHER-KEYS ...) (BLOCK HASHMAP-TO-HASHTABLE (LET # #))))
  5: (JVM::P1-LET*-VARS #S(JVM::LET/LET*-NODE :FORM NIL :COMPILAND #S(JVM::COMPILAND :NAME NIL :LAMBDA-EXPRESSION (LAMBDA NIL (SYSTEM:%DEFUN 'HASHMAP-TO-HASHTABLE (SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE ..
  6: (JVM::P1-LET/LET* (LET* ((#:G29655 #)) (SYSTEM:%DEFUN 'HASHMAP-TO-HASHTABLE #:G29655)))
  7: (JVM::P1 (LET* ((#:G29655 #)) (SYSTEM:%DEFUN 'HASHMAP-TO-HASHTABLE #:G29655)))
  8: (JVM::P1-FUNCTION-CALL (SYSTEM:%DEFUN 'HASHMAP-TO-HASHTABLE (SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE (HASHMAP &KEY # # # &ALLOW-OTHER-KEYS ...) (BLOCK HASHMAP-TO-HASHTABLE #))))
  9: (JVM::P1-BODY ((SYSTEM:%DEFUN 'HASHMAP-TO-HASHTABLE (SYSTEM:NAMED-LAMBDA HASHMAP-TO-HASHTABLE # #))))
 10: (#<FUNCTION {79F502}>)
 11: (#<FUNCTION {C49395}>)
 12: (#<FUNCTION {E4ED69}> NIL (LAMBDA NIL (DEFUN HASHMAP-TO-HASHTABLE (HASHMAP &KEY # # # &ALLOW-OTHER-KEYS ...) (LET # #))))
 13: (#<FUNCTION (LAMBDA ()) {B5506C}>)
 14: (JRUN-EXCEPTION-PROTECTED #<FUNCTION (LAMBDA ()) {B5506C}>)
 15: ((FLET SWANK-BACKEND:SWANK-COMPILE-STRING) "(defun hashmap-to-hashtable (hashmap &key (keyfun #'identity) (valfun #'identity) (invert? nil)
           &allow-other-keys &rest rest)
       (let ((keyset (#\"..