[processing] only set number min value as default if parameter is not…

… optional

python/plugins/processing/gui/NumberInputPanel.py

@@ -184,7 +184,7 @@ def __init__(self, param):
                     self.spnValue.setClearValue(float(param.defaultValue()))
                 except:
                     pass
-        elif self.param.minimum() is not None:
+        elif self.param.minimum() is not None and not self.allowing_null:
             try:
                 self.setValue(float(self.param.minimum()))
                 if not self.allowing_null: